[1.1.X] Fixed #12554 again: Corrected regression in silencing attribute...

[1.1.X] Fixed #12554 again: Corrected regression in silencing attribute lookups introduced in r12824, plus added a test for this so it doesn't regress again. 

r12834 from trunk.


git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.1.X@12835 bcc190cf-cafb-0310-a4f2-bffc1f526a37