Updated to work with Django 1.6 & Python 3.3

Adding a new user on the admin site wasn't working. 
I always got an 

```
AssertionError at /admin/users/user/add/
sensitive_post_parameters didn't receive an HttpRequest. If you are decorating a 
classmethod, be sure to use @method_decorator.
```

I found a soulution here: http://stackoverflow.com/q/19139668
I implemented it, and it works fine. 

This pull request also fixes issue #3 by jieter.