Django 1.5 Custom User Model Compatibility

I've made some little changes to make the app compatible with new Django 1.5 changes to user's model customization. Basically, instead of using django.contrib.auth.models.User, I'm calling django_facebook.utils.get_user_model().
It wraps around django.contrib.auth.get_user_model(). If the latter isn't defined, falls back to use the default User model.