[1.1.X] Fixed #11810 -- Fixed typo and errors that prevented `modifiable` from...

[1.1.X] Fixed #11810 -- Fixed typo and errors that prevented `modifiable` from working in the geographic admin.  Thanks to Rob Coup for the bug report.  Refs #12504.

Backport of r12995 from trunk.


git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.1.X@12996 bcc190cf-cafb-0310-a4f2-bffc1f526a37