Tests for Python 3.3 are failing

[jgonggrijp]

Python 3.3 is end-of-life, but I'm committed to not dropping support for anything until the next major release. I still have a minor release to do, so I'm stuck with Python 3.3. for now.

The tests are currently rather over-complicated, with nested virtualenvs and doubly-force-upgraded installations of pip et al. I'm going to try whether I can simplify things and avoid incompatible versions of pip and setuptools as a side effect. As always, help is welcome.

[jgonggrijp]

At second thought, I suggest not working on this until #61 is implemented. Leaving this open just to acknowledge the current situation.