Fix #447 - Correct django-registration installation.

Fix the django-registration setup.py syntax, but because the newest
django-registration package has an install-time dependency on Django,
for now we need to install it explicitly in dev/setup, AFTER everything
else has been installed.
Fix #447 - Cleaner solution to dependency issue.

After some reading and experimentation on various means of dealing with
install-time dependencies, it seems that these are pretty difficult to
deal with in a way that would work for us both in our dev/setup script
AND for Heroku deployments.  Therefore, I found a fork of
django-registration which has corrected the install-time dependency and
we will point at that until appropriate patches have been pulled into
the mainline repository.