Project avatar URLs in project lists are generated with full server name instead of relative

This causes a URL like:

https://git-internal.DOMAIN/uploads/project/avatar/186/teamlogo.GIF

instead of

/uploads/project/avatar/186/teamlogo.GIF

Normally, this isn't an issue, but if you have the server exposed via a proxy:

https://git-external.DOMAIN/

It causes broken image links. The other image/icon references on the page seem fine.