applied and fixed a patch from Stephane Bibould to provide per parser

* python/generator.py python/libxml.c python/libxml.py
  python/libxml_wrap.h python/types.c: applied and fixed a patch
  from Stephane Bibould to provide per parser error handlers at the
  Python level.
* python/tests/Makefile.am python/tests/ctxterror.py: added a
  regression test for it.
Daniel

python/types.c

@@ -323,6 +323,7 @@ libxml_xmlParserCtxtPtrWrap(xmlParserCtxtPtr ctxt)
         Py_INCREF(Py_None);
         return (Py_None);
     }
+
     ret =
         PyCObject_FromVoidPtrAndDesc((void *) ctxt,
                                      (char *) "xmlParserCtxtPtr", NULL);