Fixed #13000 - Use a dictionary for the error messages definition in user...

Fixed #13000 - Use a dictionary for the error messages definition in user creation and change form. Thanks for the patch, lgs.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@12785 bcc190cf-cafb-0310-a4f2-bffc1f526a37