WIP: Python3.3 - Make it compatible

Make django-browserid Python3.3 compatible.
The automatic tests say it work with Python 2.6, 2.7 and 3.3 (see the [Build Status](https://travis-ci.org/senden9/django-browserid/builds/10596540)) but with for 3.2. It should be tested manually or reviewed from other people before release/merge it.