another patch from Brent Hendricks to add new handlers with the various

* python/generator.py python/libxml.py: another patch from Brent
  Hendricks to add new handlers with the various validity contexts
* python/tests/Makefile.am python/tests/validDTD.py
  python/tests/validRNG.py python/tests/validSchemas.py: also
  added the regression tests he provided
Daniel
diff --git a/python/generator.py b/python/generator.py
index 0856d76..6144e54 100755
--- a/python/generator.py
+++ b/python/generator.py
@@ -747,6 +747,9 @@
     "inputBuffer": "ioReadWrapper",
     "parserCtxt": "parserCtxtCore",
     "xmlTextReader": "xmlTextReaderCore",
+    "ValidCtxt": "ValidCtxtCore",
+    "SchemaValidCtxt": "SchemaValidCtxtCore",
+    "relaxNgValidCtxt": "relaxNgValidCtxtCore",
 }
 classes_destructors = {
     "parserCtxt": "xmlFreeParserCtxt",