* parser.c: make sure SAX endDocument is always called as
  this could result in a Python memory leak otherwise (it's
  used to decrement ref-counting)
* python/generator.py python/libxml.c python/libxml.py
  python/libxml2-python-api.xml python/libxml2class.txt
  python/tests/error.py python/tests/xpath.py: implemented
  the suggestions made by Gary Benson and extended the tests
  to match it.
Daniel