Code review comment for lp:~abentley/testtools/expected-exception

Thanks Aaron.

I've taken your branch and:
 * Update copyright years in:
   * testcase.py
   * LICENSE
   * __init__.py
 * Update copyright years in LICENSE
 * Added to NEWS
 * Added Aaron to contributor list in README
 * Beefed up docstring
 * Re-exported from testcase/__init__.py (added to __all__)
 * Added to __all__ in testcase.py
 * Updated MatchesException to also take an optional regex
 * Updated for-test-authors.rst to describe ExpectedException

I also tried out Rob's suggestion of using MatchesException. However, the re-raise logic of the context manager, plus the way that context managers can get None for exc_type means that there is very little code re-use, so I've left things pretty much the way you wrote them.

See lp:~jml/testtools/expected-exception, or trunk rsn.