enhanced macros to avoid breaking ABI from previous versions. modified to

* genChRanges.py, chvalid.c, include/libxml/chvalid.h,
  include/libxml/parserInternals.h: enhanced macros to avoid
  breaking ABI from previous versions.
* catalog.c, parser.c, tree.c: modified to use IS_* macros
  defined in parserInternals.h.  Makes maintenance much easier.
* testHTML.c, testSAX.c, python/libxml.c: minor fixes to avoid
  compilation warnings
* configuration.in: fixed pushHTML test error; enhanced for
  better devel (me) testing

python/libxml.c

@@ -1061,6 +1061,7 @@ static xmlSAXHandler pythonSaxHandler = {
     1,
     NULL,			/* TODO mograte to SAX2 */
     NULL,
+    NULL,
     NULL
 };