updated the docs and rebuild releasing 2.6.21 removed

* NEWS elfgcchack.h testapi.c doc/*: updated the docs and rebuild
  releasing 2.6.21
* include/libxml/threads.h threads.c: removed xmlIsThreadsEnabled()
* threads.c include/libxml/threads.h xmllint.c: added the more
  generic xmlHasFeature() as suggested by Bjorn Reese, xmllint uses it.
Daniel
diff --git a/doc/APIchunk26.html b/doc/APIchunk26.html
index 3aefd61..8a0befa 100644
--- a/doc/APIchunk26.html
+++ b/doc/APIchunk26.html
@@ -85,6 +85,7 @@
 <a href="html/libxml-schemasInternals.html#XML_SCHEMAS_FACET_UNKNOWN">XML_SCHEMAS_FACET_UNKNOWN</a><br />
 <a href="html/libxml-HTMLparser.html#htmlCtxtUseOptions">htmlCtxtUseOptions</a><br />
 <a href="html/libxml-parser.html#xmlCtxtUseOptions">xmlCtxtUseOptions</a><br />
+<a href="html/libxml-parser.html#xmlHasFeature">xmlHasFeature</a><br />
 <a href="html/libxml-xmlunicode.html#xmlUCSIsBlock">xmlUCSIsBlock</a><br />
 <a href="html/libxml-xmlunicode.html#xmlUCSIsCat">xmlUCSIsCat</a><br />
 </dd><dt>unless</dt><dd><a href="html/libxml-HTMLparser.html#htmlSAXParseDoc">htmlSAXParseDoc</a><br />