Source page still exists for deleted repository (BB-1451)

I moved some repositories from the 'mg' user to the 'aragost' user and put in redirect. This mostly works, except that URLs like

https://bitbucket.org/mg/kick-start/src/

show the source page (with no content) instead of the redirection notice. If a repository had set the source page as the default page, then the redirect to the source page still takes place:

https://bitbucket.org/mg/remoteinfo/