Code review comment for lp:~brian-murray/launchpad/limited-subscriptions-page

There's one thing which I overlooked in my analysis above: ReturnToReferrerMixin._return_url will return self.request.getHeader('referer') when a _return_url is not present in the request. So there must be something that is stripping referrers out of my requests. I'll figure it out; sorry for the false alarm.