[1.1.X] Fixed #12024: Changed admin code to avoid raising an exception when a field listed

in raw_id_fields has limit_choices_to specified as a Q object.

Tweaked a test to trigger the condition and verify the fix.

Finally, documented that limit_choices_to specified as a Q object has no effect
on the choices available for fields listed in raw_id_fields, and removed another
incorrect note that claimed limit_choices_to had no effect on inlines in the admin. 

r12728 from trunk.


git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.1.X@12729 bcc190cf-cafb-0310-a4f2-bffc1f526a37