Fix for copyright not showing up in RSS feed

Code coverage showed I was missing a line, because I'd used
the wrong function name. Once I fixed that, I discovered a
bug in the way I was getting the date for the copyright.
Fixing bad import

I used to have a backport of assignment_tag for Django 1.3.
I don't care about Django 1.3 any more, since it's no longer
supported.
Ensure tests actually render content