Swappable User model

I'm working on support for [custom user model](https://docs.djangoproject.com/en/dev/topics/auth/customizing/#auth-custom-user) as described in the docs for the upcoming Django 1.5.

My idea is to first get a working solution that allows for extending normal User model (subclassing ``django.contrib.auth.models.AbstractUser``) and after that possibly replacing it with a totally custom one that is based on the [AbstractBaseUser](https://docs.djangoproject.com/en/dev/topics/auth/customizing/#django.contrib.auth.models.AbstractBaseUser).

Is this something you would like to be included in the app? Any feedback and testing greatly appreciated.