backport of the enhanced unittest testing framework in Python 2.7

 unittest2 is an enhanced version of unittest including a
 standard test runner (automatic test discovery), class and
 module level fixtures (``setUpClass`` / ``setUpModule`` etc),
 many powerful new assert methods, better resource management
 with ``addCleanups`` and a host of other new features. These new
 features are *all* going into the Python version of unittest in
 Python 2.7 and Python 3.2. The point of unittest2 is that it
 works with Python 2.4 - 2.6; you can use it now.