change a small bit in the way valididy error messages get initialized

* parserInternals.c: change a small bit in the way valididy
  error messages get initialized
* python/TODO python/libxml.c python/libxml2-python-api.xml
  python/libxml2class.txt python/libxml_wrap.h python/types.c:
  added some memory debugging to track leaks at the libxml2 level
* python/tests/*.py: changed all tests to check for leaks,
  there is just one left in XPath extension registrations.
daniel

python/tests/xpathext.py

@@ -2,6 +2,9 @@
 import sys
 import libxml2
 
+# Memory debug specific
+libxml2.debugMemory(1)
+
 def foo(x):
     return x + 1
 
@@ -35,4 +38,12 @@ while i > 0:
 	sys.exit(1)
     i = i - 1
 doc.freeDoc()
-print "OK"
+del ctxt
+
+# Memory debug specific
+libxml2.cleanupParser()
+if libxml2.debugMemory(1) == 0:
+    print "OK"
+else:
+    print "Memory leak %d bytes" % (libxml2.debugMemory(1))
+    libxml2.dumpMemory()