more accessor classes for the parser context, allow to switch on and check

* python/TODO python/generator.py python/libxml2-python-api.xml
  python/libxml2class.txt: more accessor classes for the parser
  context, allow to switch on and check validity
* python/tests/Makefile.am python/tests/error.py
  python/tests/invalid.xml python/tests/valid.xml
  python/tests/validate.py: attded more test and and added error.py
  which I forgot to commit in the last step
Daniel

python/tests/error.py

@@ -0,0 +1,30 @@
+#!/usr/bin/python -u
+#
+# This test exercise the redirection of error messages with a
+# functions defined in Python.
+#
+import sys
+import libxml2
+
+expect='--> warning: --> failed to load external entity "missing.xml"\n'
+err=""
+def callback(ctx, str):
+     global err
+
+     err = err + "%s %s" % (ctx, str)
+
+libxml2.registerErrorHandler(callback, "-->")
+doc = libxml2.parseFile("missing.xml")
+if err != expect:
+    print "error"
+    print "received %s" %(err)
+    print "expected %s" %(expect)
+    sys.exit(1)
+
+i = 10000
+while i > 0:
+    doc = libxml2.parseFile("missing.xml")
+    err = ""
+    i = i - 1
+
+print "OK"