A few Django 1.5-friendly updates

Hey Jannis,

These changes were hurriedly scrawled while integrating this as a proof of concept into a Django 1.5 project utilising a custom User model. I should perhaps have put them on a separate branch. I figured we needed to maintain support for 1.4? They are largely untested, and I doubt I'll get around to updating the unit tests for this app. Thought I'd ping you in case the changes are a helpful starting point for someone who has more time to test thoroughly...

Simon