augmented types supported a number of new bug fixes and documentation

* gentest.py testapi.c: augmented types supported
* HTMLtree.c tree.c xmlreader.c xmlwriter.c: a number of new
  bug fixes and documentation updates.
Daniel
diff --git a/xmlreader.c b/xmlreader.c
index 8e765c3..a5aba32 100644
--- a/xmlreader.c
+++ b/xmlreader.c
@@ -4213,8 +4213,8 @@
 xmlTextReaderGetErrorHandler(xmlTextReaderPtr reader, 
 			     xmlTextReaderErrorFunc *f, 
 			     void **arg) {
-    *f = reader->errorFunc;
-    *arg = reader->errorFuncArg;
+    if (f != NULL) *f = reader->errorFunc;
+    if (arg != NULL) *arg = reader->errorFuncArg;
 }