Links in RSS feed do not use absolute URLs

This is a duplicate of FE-1991 (which was closed as Fixed for unknown reason).

RSS feeds from FishEye use relative URLs instead of absolute (no FE base URL: href="/browse/..."). As a result, source, history and diff links are absolutely useless being open not in the original site context.

See the problem in action here: http://forums.openpilot.org/topic/7405-openpilot-ostxpid-module-merge-branch-next-into-ostxpid-module/

Unfortunately, the template is hard-coded in a tag file of source code, so no easy way to fix it ourselves.