user as AUTH_USER_MODEL

Should now grab AUTH_USER_MODEL if it's defined.

Whether it will behave nicely for a custom user model is another question.  I ran into enough issues hooking a custom user up that I plan to stick with the regular Django user model until my needs are greater than they are now.

Issue 1: LazyAdminSite.lazy_registration() gets a request to unregister the default User when it hasn't first been registered, and we get a NotRegistered exception.

Issue 2: If I comment out admin.autodiscover(), things seem to work until anything relating to user accounts happens, then we get a AttributeError, saying Manager isn't available; User has been swapped for 'myApp.CustomUser'.