Compatibility fix for JSON emitter with Django 1.5
Fixed compatibility with Django 1.5
Compatibility with swappable User model in Django 1.5
Django 1.5 compatibility

From https://bitbucket.org/spookylukey/django-piston/commits/all

- Compatibility fix for JSON emitter with Django 1.5
- Fixed compatibility with Django 1.5
- Compatibility with swappable User model in Django 1.5