fixed xmlXPathReturnString to cater for NULL pointer (bug 129561) added

* include/libxml/xpathInternals.h: fixed xmlXPathReturnString
  to cater for NULL pointer (bug 129561)
* globals.c: added comment to suppress documentation warning
* doc/apibuild.py: fixed problem which caused last APIchunkxx.html
  to be lost.  Rebuilt doc/* (including adding APIchunk26.html)
diff --git a/doc/APIconstructors.html b/doc/APIconstructors.html
index 5220d77..dbfe0f6 100644
--- a/doc/APIconstructors.html
+++ b/doc/APIconstructors.html
@@ -17,6 +17,7 @@
 <a href="html/libxml-HTMLtree.html#htmlGetMetaEncoding">htmlGetMetaEncoding</a><br />
 <a href="html/libxml-xmlreader.html#xmlTextReaderConstLocalName">xmlTextReaderConstLocalName</a><br />
 <a href="html/libxml-parserInternals.html#xmlParseName">xmlParseName</a><br />
+<a href="html/libxml-SAX.html#getSystemId">getSystemId</a><br />
 <a href="html/libxml-parserInternals.html#namePop">namePop</a><br />
 <a href="html/libxml-parser.html#xmlStrcasestr">xmlStrcasestr</a><br />
 <a href="html/libxml-dict.html#xmlDictLookup">xmlDictLookup</a><br />
@@ -26,7 +27,6 @@
 <a href="html/libxml-parserInternals.html#xmlParseEncodingDecl">xmlParseEncodingDecl</a><br />
 <a href="html/libxml-tree.html#xmlBufferContent">xmlBufferContent</a><br />
 <a href="html/libxml-xmlreader.html#xmlTextReaderConstString">xmlTextReaderConstString</a><br />
-<a href="html/libxml-SAX.html#getSystemId">getSystemId</a><br />
 <a href="html/libxml-catalog.html#xmlCatalogGetSystem">xmlCatalogGetSystem</a><br />
 <a href="html/libxml-SAX2.html#xmlSAX2GetPublicId">xmlSAX2GetPublicId</a><br />
 <a href="html/libxml-xmlreader.html#xmlTextReaderConstName">xmlTextReaderConstName</a><br />
@@ -56,7 +56,6 @@
 <a href="html/libxml-xpathInternals.html#xmlXPathPopNumber">xmlXPathPopNumber</a><br />
 <a href="html/libxml-xpath.html#xmlXPathCastBooleanToNumber">xmlXPathCastBooleanToNumber</a><br />
 </p><h2>Type htmlDocPtr:</h2><p><a href="html/libxml-HTMLparser.html#htmlParseDoc">htmlParseDoc</a><br />
-<a href="html/libxml-HTMLparser.html#htmlReadIO">htmlReadIO</a><br />
 <a href="html/libxml-HTMLparser.html#htmlCtxtReadFile">htmlCtxtReadFile</a><br />
 <a href="html/libxml-HTMLparser.html#htmlSAXParseDoc">htmlSAXParseDoc</a><br />
 <a href="html/libxml-HTMLparser.html#htmlCtxtReadFd">htmlCtxtReadFd</a><br />
@@ -70,9 +69,10 @@
 <a href="html/libxml-HTMLparser.html#htmlParseFile">htmlParseFile</a><br />
 <a href="html/libxml-HTMLparser.html#htmlReadDoc">htmlReadDoc</a><br />
 <a href="html/libxml-HTMLtree.html#htmlNewDoc">htmlNewDoc</a><br />
+<a href="html/libxml-HTMLparser.html#htmlReadIO">htmlReadIO</a><br />
 <a href="html/libxml-HTMLparser.html#htmlReadFd">htmlReadFd</a><br />
-</p><h2>Type htmlParserCtxtPtr:</h2><p><a href="html/libxml-parserInternals.html#htmlCreateFileParserCtxt">htmlCreateFileParserCtxt</a><br />
-<a href="html/libxml-HTMLparser.html#htmlCreatePushParserCtxt">htmlCreatePushParserCtxt</a><br />
+</p><h2>Type htmlParserCtxtPtr:</h2><p><a href="html/libxml-HTMLparser.html#htmlCreatePushParserCtxt">htmlCreatePushParserCtxt</a><br />
+<a href="html/libxml-parserInternals.html#htmlCreateFileParserCtxt">htmlCreateFileParserCtxt</a><br />
 <a href="html/libxml-HTMLparser.html#htmlCreateMemoryParserCtxt">htmlCreateMemoryParserCtxt</a><br />
 </p><h2>Type htmlStatus:</h2><p><a href="html/libxml-HTMLparser.html#htmlElementStatusHere">htmlElementStatusHere</a><br />
 <a href="html/libxml-HTMLparser.html#htmlAttrAllowed">htmlAttrAllowed</a><br />
@@ -82,12 +82,12 @@
 </p><h2>Type unsigned long:</h2><p><a href="html/libxml-parser.html#xmlParserFindNodeInfoIndex">xmlParserFindNodeInfoIndex</a><br />
 </p><h2>Type void *:</h2><p><a href="html/libxml-nanohttp.html#xmlNanoHTTPMethod">xmlNanoHTTPMethod</a><br />
 <a href="html/libxml-xmlmemory.html#xmlMemRealloc">xmlMemRealloc</a><br />
+<a href="html/libxml-list.html#xmlLinkGetData">xmlLinkGetData</a><br />
 <a href="html/libxml-hash.html#xmlHashLookup3">xmlHashLookup3</a><br />
 <a href="html/libxml-xmlmemory.html#xmlReallocFunc">xmlReallocFunc</a><br />
 <a href="html/libxml-nanoftp.html#xmlNanoFTPConnectTo">xmlNanoFTPConnectTo</a><br />
 <a href="html/libxml-xmlIO.html#xmlOutputOpenCallback">xmlOutputOpenCallback</a><br />
 <a href="html/libxml-hash.html#xmlHashLookup2">xmlHashLookup2</a><br />
-<a href="html/libxml-list.html#xmlLinkGetData">xmlLinkGetData</a><br />
 <a href="html/libxml-hash.html#xmlHashLookup">xmlHashLookup</a><br />
 <a href="html/libxml-hash.html#xmlHashQLookup">xmlHashQLookup</a><br />
 <a href="html/libxml-list.html#xmlListReverseSearch">xmlListReverseSearch</a><br />
@@ -126,9 +126,9 @@
 <a href="html/libxml-tree.html#xmlNewNsPropEatName">xmlNewNsPropEatName</a><br />
 <a href="html/libxml-tree.html#xmlCopyProp">xmlCopyProp</a><br />
 <a href="html/libxml-tree.html#xmlSetProp">xmlSetProp</a><br />
-</p><h2>Type xmlAttributePtr:</h2><p><a href="html/libxml-valid.html#xmlGetDtdAttrDesc">xmlGetDtdAttrDesc</a><br />
-<a href="html/libxml-valid.html#xmlAddAttributeDecl">xmlAddAttributeDecl</a><br />
+</p><h2>Type xmlAttributePtr:</h2><p><a href="html/libxml-valid.html#xmlAddAttributeDecl">xmlAddAttributeDecl</a><br />
 <a href="html/libxml-valid.html#xmlGetDtdQAttrDesc">xmlGetDtdQAttrDesc</a><br />
+<a href="html/libxml-valid.html#xmlGetDtdAttrDesc">xmlGetDtdAttrDesc</a><br />
 </p><h2>Type xmlAttributeTablePtr:</h2><p><a href="html/libxml-valid.html#xmlCopyAttributeTable">xmlCopyAttributeTable</a><br />
 </p><h2>Type xmlAutomataPtr:</h2><p><a href="html/libxml-xmlautomata.html#xmlNewAutomata">xmlNewAutomata</a><br />
 </p><h2>Type xmlAutomataStatePtr:</h2><p><a href="html/libxml-xmlautomata.html#xmlAutomataNewCountedTrans">xmlAutomataNewCountedTrans</a><br />
@@ -149,18 +149,18 @@
 </p><h2>Type xmlCatalogAllow:</h2><p><a href="html/libxml-catalog.html#xmlCatalogGetDefaults">xmlCatalogGetDefaults</a><br />
 </p><h2>Type xmlCatalogPrefer:</h2><p><a href="html/libxml-catalog.html#xmlCatalogSetDefaultPrefer">xmlCatalogSetDefaultPrefer</a><br />
 </p><h2>Type xmlCatalogPtr:</h2><p><a href="html/libxml-catalog.html#xmlLoadSGMLSuperCatalog">xmlLoadSGMLSuperCatalog</a><br />
-<a href="html/libxml-catalog.html#xmlLoadACatalog">xmlLoadACatalog</a><br />
 <a href="html/libxml-catalog.html#xmlNewCatalog">xmlNewCatalog</a><br />
+<a href="html/libxml-catalog.html#xmlLoadACatalog">xmlLoadACatalog</a><br />
 </p><h2>Type xmlChar:</h2><p><a href="html/libxml-parserInternals.html#xmlPopInput">xmlPopInput</a><br />
 </p><h2>Type xmlChar *:</h2><p><a href="html/libxml-tree.html#xmlNodeGetBase">xmlNodeGetBase</a><br />
 <a href="html/libxml-parserInternals.html#xmlScanName">xmlScanName</a><br />
 <a href="html/libxml-valid.html#xmlValidCtxtNormalizeAttributeValue">xmlValidCtxtNormalizeAttributeValue</a><br />
 <a href="html/libxml-tree.html#xmlGetNoNsProp">xmlGetNoNsProp</a><br />
-<a href="html/libxml-parser.html#xmlStrcat">xmlStrcat</a><br />
 <a href="html/libxml-xmlreader.html#xmlTextReaderReadOuterXml">xmlTextReaderReadOuterXml</a><br />
 <a href="html/libxml-tree.html#xmlNodeListGetRawString">xmlNodeListGetRawString</a><br />
 <a href="html/libxml-xmlreader.html#xmlTextReaderNamespaceUri">xmlTextReaderNamespaceUri</a><br />
 <a href="html/libxml-catalog.html#xmlCatalogResolvePublic">xmlCatalogResolvePublic</a><br />
+<a href="html/libxml-parser.html#xmlStrcat">xmlStrcat</a><br />
 <a href="html/libxml-xpathInternals.html#xmlXPathPopString">xmlXPathPopString</a><br />
 <a href="html/libxml-xmlreader.html#xmlTextReaderReadString">xmlTextReaderReadString</a><br />
 <a href="html/libxml-catalog.html#xmlCatalogResolveSystem">xmlCatalogResolveSystem</a><br />
@@ -178,6 +178,7 @@
 <a href="html/libxml-parserInternals.html#xmlStringDecodeEntities">xmlStringDecodeEntities</a><br />
 <a href="html/libxml-parserInternals.html#xmlParseEncName">xmlParseEncName</a><br />
 <a href="html/libxml-xmlreader.html#xmlTextReaderPrefix">xmlTextReaderPrefix</a><br />
+<a href="html/libxml-parserInternals.html#xmlDecodeEntities">xmlDecodeEntities</a><br />
 <a href="html/libxml-xpath.html#xmlXPathCastNumberToString">xmlXPathCastNumberToString</a><br />
 <a href="html/libxml-parserInternals.html#xmlParseNmtoken">xmlParseNmtoken</a><br />
 <a href="html/libxml-xmlreader.html#xmlTextReaderLocatorBaseURI">xmlTextReaderLocatorBaseURI</a><br />
@@ -189,7 +190,6 @@
 <a href="html/libxml-entities.html#xmlEncodeSpecialChars">xmlEncodeSpecialChars</a><br />
 <a href="html/libxml-uri.html#xmlURIEscapeStr">xmlURIEscapeStr</a><br />
 <a href="html/libxml-tree.html#xmlGetNsProp">xmlGetNsProp</a><br />
-<a href="html/libxml-parserInternals.html#xmlDecodeEntities">xmlDecodeEntities</a><br />
 <a href="html/libxml-xpath.html#xmlXPathCastNodeToString">xmlXPathCastNodeToString</a><br />
 <a href="html/libxml-parserInternals.html#xmlNamespaceParseNCName">xmlNamespaceParseNCName</a><br />
 <a href="html/libxml-catalog.html#xmlCatalogResolveURI">xmlCatalogResolveURI</a><br />
@@ -237,8 +237,8 @@
 </p><h2>Type xmlCharEncoding:</h2><p><a href="html/libxml-encoding.html#xmlDetectCharEncoding">xmlDetectCharEncoding</a><br />
 <a href="html/libxml-encoding.html#xmlParseCharEncoding">xmlParseCharEncoding</a><br />
 </p><h2>Type xmlCharEncodingHandlerPtr:</h2><p><a href="html/libxml-encoding.html#xmlGetCharEncodingHandler">xmlGetCharEncodingHandler</a><br />
-<a href="html/libxml-encoding.html#xmlFindCharEncodingHandler">xmlFindCharEncodingHandler</a><br />
 <a href="html/libxml-encoding.html#xmlNewCharEncodingHandler">xmlNewCharEncodingHandler</a><br />
+<a href="html/libxml-encoding.html#xmlFindCharEncodingHandler">xmlFindCharEncodingHandler</a><br />
 </p><h2>Type xmlDeregisterNodeFunc:</h2><p><a href="html/libxml-globals.html#xmlThrDefDeregisterNodeDefault">xmlThrDefDeregisterNodeDefault</a><br />
 <a href="html/libxml-globals.html#xmlDeregisterNodeDefault">xmlDeregisterNodeDefault</a><br />
 </p><h2>Type xmlDictPtr:</h2><p><a href="html/libxml-dict.html#xmlDictCreate">xmlDictCreate</a><br />
@@ -247,8 +247,8 @@
 <a href="html/libxml-parser.html#xmlSAXParseMemoryWithData">xmlSAXParseMemoryWithData</a><br />
 <a href="html/libxml-parser.html#xmlSAXParseEntity">xmlSAXParseEntity</a><br />
 <a href="html/libxml-parser.html#xmlParseEntity">xmlParseEntity</a><br />
-<a href="html/libxml-parser.html#xmlRecoverDoc">xmlRecoverDoc</a><br />
 <a href="html/libxml-parser.html#xmlSAXParseFileWithData">xmlSAXParseFileWithData</a><br />
+<a href="html/libxml-parser.html#xmlRecoverDoc">xmlRecoverDoc</a><br />
 <a href="html/libxml-parser.html#xmlReadDoc">xmlReadDoc</a><br />
 <a href="html/libxml-parser.html#xmlReadMemory">xmlReadMemory</a><br />
 <a href="html/libxml-parser.html#xmlCtxtReadIO">xmlCtxtReadIO</a><br />
@@ -256,23 +256,23 @@
 <a href="html/libxml-parser.html#xmlReadFile">xmlReadFile</a><br />
 <a href="html/libxml-parser.html#xmlRecoverFile">xmlRecoverFile</a><br />
 <a href="html/libxml-parser.html#xmlSAXParseDoc">xmlSAXParseDoc</a><br />
-<a href="html/libxml-catalog.html#xmlParseCatalogFile">xmlParseCatalogFile</a><br />
 <a href="html/libxml-parser.html#xmlCtxtReadFile">xmlCtxtReadFile</a><br />
 <a href="html/libxml-parser.html#xmlCtxtReadFd">xmlCtxtReadFd</a><br />
 <a href="html/libxml-parser.html#xmlReadIO">xmlReadIO</a><br />
 <a href="html/libxml-tree.html#xmlCopyDoc">xmlCopyDoc</a><br />
 <a href="html/libxml-parser.html#xmlCtxtReadMemory">xmlCtxtReadMemory</a><br />
 <a href="html/libxml-parser.html#xmlReadFd">xmlReadFd</a><br />
+<a href="html/libxml-catalog.html#xmlParseCatalogFile">xmlParseCatalogFile</a><br />
 <a href="html/libxml-parser.html#xmlCtxtReadDoc">xmlCtxtReadDoc</a><br />
 <a href="html/libxml-parser.html#xmlParseMemory">xmlParseMemory</a><br />
 <a href="html/libxml-parser.html#xmlSAXParseFile">xmlSAXParseFile</a><br />
 <a href="html/libxml-parser.html#xmlParseFile">xmlParseFile</a><br />
 <a href="html/libxml-xmlreader.html#xmlTextReaderCurrentDoc">xmlTextReaderCurrentDoc</a><br />
 <a href="html/libxml-tree.html#xmlNewDoc">xmlNewDoc</a><br />
-</p><h2>Type xmlDtdPtr:</h2><p><a href="html/libxml-parser.html#xmlIOParseDTD">xmlIOParseDTD</a><br />
-<a href="html/libxml-tree.html#xmlCopyDtd">xmlCopyDtd</a><br />
+</p><h2>Type xmlDtdPtr:</h2><p><a href="html/libxml-tree.html#xmlCopyDtd">xmlCopyDtd</a><br />
 <a href="html/libxml-tree.html#xmlGetIntSubset">xmlGetIntSubset</a><br />
 <a href="html/libxml-tree.html#xmlCreateIntSubset">xmlCreateIntSubset</a><br />
+<a href="html/libxml-parser.html#xmlIOParseDTD">xmlIOParseDTD</a><br />
 <a href="html/libxml-parser.html#xmlSAXParseDTD">xmlSAXParseDTD</a><br />
 <a href="html/libxml-parser.html#xmlParseDTD">xmlParseDTD</a><br />
 <a href="html/libxml-tree.html#xmlNewDtd">xmlNewDtd</a><br />
@@ -406,9 +406,9 @@
 <a href="html/libxml-parser.html#xmlCreateIOParserCtxt">xmlCreateIOParserCtxt</a><br />
 <a href="html/libxml-parserInternals.html#xmlCreateFileParserCtxt">xmlCreateFileParserCtxt</a><br />
 <a href="html/libxml-parser.html#xmlCreateDocParserCtxt">xmlCreateDocParserCtxt</a><br />
+<a href="html/libxml-parserInternals.html#xmlCreateEntityParserCtxt">xmlCreateEntityParserCtxt</a><br />
 <a href="html/libxml-parser.html#xmlCreatePushParserCtxt">xmlCreatePushParserCtxt</a><br />
 <a href="html/libxml-parser.html#xmlNewParserCtxt">xmlNewParserCtxt</a><br />
-<a href="html/libxml-parserInternals.html#xmlCreateEntityParserCtxt">xmlCreateEntityParserCtxt</a><br />
 </p><h2>Type xmlParserInputBufferPtr:</h2><p><a href="html/libxml-xmlIO.html#xmlParserInputBufferCreateFilename">xmlParserInputBufferCreateFilename</a><br />
 <a href="html/libxml-xmlIO.html#xmlParserInputBufferCreateMem">xmlParserInputBufferCreateMem</a><br />
 <a href="html/libxml-xmlIO.html#xmlAllocParserInputBuffer">xmlAllocParserInputBuffer</a><br />
@@ -452,8 +452,8 @@
 </p><h2>Type xmlSchemaValidCtxtPtr:</h2><p><a href="html/libxml-xmlschemas.html#xmlSchemaNewValidCtxt">xmlSchemaNewValidCtxt</a><br />
 </p><h2>Type xmlTextReaderPtr:</h2><p><a href="html/libxml-xmlreader.html#xmlReaderForFile">xmlReaderForFile</a><br />
 <a href="html/libxml-xmlreader.html#xmlReaderForIO">xmlReaderForIO</a><br />
-<a href="html/libxml-xmlreader.html#xmlReaderForFd">xmlReaderForFd</a><br />
 <a href="html/libxml-xmlreader.html#xmlNewTextReader">xmlNewTextReader</a><br />
+<a href="html/libxml-xmlreader.html#xmlReaderForFd">xmlReaderForFd</a><br />
 <a href="html/libxml-xmlreader.html#xmlReaderWalker">xmlReaderWalker</a><br />
 <a href="html/libxml-xmlreader.html#xmlNewTextReaderFilename">xmlNewTextReaderFilename</a><br />
 <a href="html/libxml-xmlreader.html#xmlReaderForDoc">xmlReaderForDoc</a><br />