Django 1.7 support

[thisiscam]

I just pushed some really bad hack for this repo to work under django 1.7. Don't know if anyone is still using this package and might want this update. It was really bad practice, I basically copied the compatible method version from django 1.4, and if there's anyone who familiar with django might be able to fix the issue with a better practice.
Here's the fix: https://github.com/thisiscam/django-relationships