[1.0.X] Merged [9682], [9683] and [9684] from trunk. These were changes...

[1.0.X] Merged [9682], [9683] and [9684] from trunk. These were changes dealing with documenting and adding a helpful error message for the quirk of admin users needing 'change user' permission to add users. Refs #9866

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.0.X@9685 bcc190cf-cafb-0310-a4f2-bffc1f526a37