Eliminate unittest2 and add support for Python 3.3

This eliminates the dependency on unittest2, which is not available
for Python 3, by replacing the only Python 2.6-incompatible assert.
It also adds testing against Python 3.3 and Python 3.4, and I have
confirmed that tests now run against Python 3.3.  The trove
classification has also been updated to reflect the Python 3.3 and
3.4 support.