Python 3 support

Drops support for:
 * django 1.2
 * python 2.5

Adds tested support for:
 * django 1.5+
 * python 3.2
 * python 3.3

started from @tow's work at #231, fixed some things, vendored `six` so we can use it with django < 1.5, and made everything awesome.

All the tests now pass! Time for someone to review this before I merge it in. .. Please? :)