setup.py: Update trove classifiers to Python 2.7, 3.2, and 3.3
.travis.yml: Test on Python 3.3 as well as 2.7 and 3.2

If we advertise 3.3 support in setup.py, we should test for it.
tox.ini: Test on Python 3.3 as well as 2.7 and 3.2

I just copied the 3.2 environment for 3.3.  They should be similar,
but it's possible some packages have extra issues on 3.3.