Override redirect middleware to issue 302s.

Still a bit hackish until django 1.6.

Note: this code is basically just copying django.contrib.redirects, but with changes on lines 24 and 25 to issue 302 instead of 301 and 404 instead of 410, so that they will not be permanently cached in browsers.  Once we're on django 1.6, there will be a nicer way to override this, without code duplication.