patch from Joachim Bauch + cleanup for Relax NG error callbacks in python

* python/generator.py python/libxml.c python/libxml2class.txt:
  patch from Joachim Bauch + cleanup for Relax NG error callbacks
  in python
Daniel
diff --git a/python/generator.py b/python/generator.py
index b444443..c65728c 100755
--- a/python/generator.py
+++ b/python/generator.py
@@ -300,6 +300,9 @@
         return 1
 #    if name[0:11] == "xmlXPathNew":
 #        return 1
+    # the next function is defined in libxml.c
+    if name == "xmlRelaxNGFreeValidCtxt":
+        return 1
     return 0
 
 def print_function_wrapper(name, output, export, include):