[1.0.X] Fixed #10413: RelatedManager.add no longer fails silenty when trying...

[1.0.X] Fixed #10413: RelatedManager.add no longer fails silenty when trying to add an object of the wrong type. Thanks, dgouldin.

Backport of r10226 from trunk.


git-svn-id: http://code.djangoproject.com/svn/django/branches/releases/1.0.X@10293 bcc190cf-cafb-0310-a4f2-bffc1f526a37