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/tests/ctxterror.py

@@ -0,0 +1,55 @@
+#!/usr/bin/python -u
+#
+# This test exercise the redirection of error messages with a
+# functions defined in Python.
+#
+import sys
+import libxml2
+
+# Memory debug specific
+libxml2.debugMemory(1)
+
+expect="""--> Opening and ending tag mismatch: x and y
+"""
+
+err=""
+def callback(ctx, str):
+     global err
+
+     err = err + "%s %s" % (ctx, str)
+
+s = """<x></y>"""
+
+parserCtxt = libxml2.createPushParser(None,"",0,"test.xml")
+parserCtxt.registerErrorHandler(callback, "-->")
+parserCtxt.registerWarningHandler(callback, "-->")
+parserCtxt.parseChunk(s,len(s),1)
+doc = parserCtxt.doc()
+doc.freeDoc()
+parserCtxt = None
+
+if err != expect:
+    print "error"
+    print "received %s" %(err)
+    print "expected %s" %(expect)
+    sys.exit(1)
+
+i = 10000
+while i > 0:
+    parserCtxt = libxml2.createPushParser(None,"",0,"test.xml")
+    parserCtxt.registerErrorHandler(callback, "-->")
+    parserCtxt.registerWarningHandler(callback, "-->")
+    parserCtxt.parseChunk(s,len(s),1)
+    doc = parserCtxt.doc()
+    doc.freeDoc()
+    parserCtxt = None
+    err = ""
+    i = i - 1
+
+# Memory debug specific
+libxml2.cleanupParser()
+if libxml2.debugMemory(1) == 0:
+    print "OK"
+else:
+    print "Memory leak %d bytes" % (libxml2.debugMemory(1))
+    libxml2.dumpMemory()