Fixed #5559: instances sent via post-save signals no longer have pks of None....

Fixed #5559: instances sent via post-save signals no longer have pks of None. Thanks, Joseph Kocherhans.

git-svn-id: http://code.djangoproject.com/svn/django/trunk@6411 bcc190cf-cafb-0310-a4f2-bffc1f526a37