convenience change try to avoid calling libxml2 cleanup function directly

* configure.in: convenience change
* python/libxsl.py python/libxslt-python-api.xml python/libxslt.c:
  try to avoid calling libxml2 cleanup function directly but go
  though the python wrapper of libxml2 for memory debug accounting.
Daniel

python/libxsl.py

@@ -84,6 +84,11 @@ class extensionModule:
         """Callback function when a transformation using it finishes"""
 	pass
 
+def cleanup():
+    """Cleanup all libxslt and libxml2 memory allocated"""
+    libxsltmod.xsltPythonCleanup()
+    libxml2.cleanupParser()
+
 #
 # Everything below this point is automatically generated
 #