[1.2.X] Fixed #11058 - list_display_links doesn't allow callables not defined in the model

Thanks to dvine for the report and julien for the patch.

Backport of [15619] from trunk.

git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.2.X@15621 bcc190cf-cafb-0310-a4f2-bffc1f526a37