Better refspoofing

Not sure if we want to do this or not, but it may be a good idea to do better referrer spoofing instead of just blocking referrer all together (which is disabled by default because some sites refuse to serve images/media with no referer). The RefSpoof extension has a mode to set the referrer to the document root of a site. This code may be useful to assimilate, or we can just encourage people to install that extension if the default behavior doesn't work for them. It is possible this "set to root" site will still break sites that expect image refs to come from other paths on the site only... In this case, refspoof's complete functionality may be a good idea.

[Automatically added by flyspray2trac: Operating System: All]