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/APIchunk12.html b/doc/APIchunk12.html
index a3a22f7..9d1944e 100644
--- a/doc/APIchunk12.html
+++ b/doc/APIchunk12.html
@@ -420,7 +420,7 @@
 <a href="html/libxml-xmlregexp.html#xmlExpDump">xmlExpDump</a><br />
 <a href="html/libxml-xmlregexp.html#xmlExpMaxToken">xmlExpMaxToken</a><br />
 <a href="html/libxml-xmlerror.html#xmlGetLastError">xmlGetLastError</a><br />
-<a href="html/libxml-threads.html#xmlIsThreadsEnabled">xmlIsThreadsEnabled</a><br />
+<a href="html/libxml-parser.html#xmlHasFeature">xmlHasFeature</a><br />
 <a href="html/libxml-pattern.html#xmlPatterncompile">xmlPatterncompile</a><br />
 <a href="html/libxml-xmlregexp.html#xmlRegexpCompile">xmlRegexpCompile</a><br />
 <a href="html/libxml-xmlregexp.html#xmlRegexpExec">xmlRegexpExec</a><br />