Fixed #3011 -- Added swappable auth.User models.

      Thanks to the many people that contributed to the development and review of
this patch, including (but not limited to) Jacob Kaplan-Moss, Anssi
Kääriäinen, Ramiro Morales, Preston Holmes, Josh Ourisman, Thomas Sutton,
and Roger Barnes, as well as the many, many people who have contributed to
the design discussion around this ticket over many years.

Squashed commit of the following:

commit d84749a0f034a0a6906d20df047086b1219040d0
Merge: 531e771 7c11b1a
Author: Russell Keith-Magee <russell@keith-magee.com>
Date:   Wed Sep 26 18:37:04 2012 +0800

    Merge remote-tracking branch 'django/master' into t3011

commit 531e7715da545f930c49919a19e954d41c59b446
Merge: 29d1abb 1f84b04
Author: Russell Keith-Magee <russell@keith-magee.com>
Date:   Wed Sep 26 07:09:23 2012 +0800

    Merged recent trunk changes.

commit 29d1abbe351fd5da855fe5ce09e24227d90ddc91
Merge: 8a527dd 54c81a1
Author: Russell Keith-Magee <russell@keith-magee.com>
Date:   Mon Se