- Display mirror domain instead of an arbitrary index (which could change)
- Fix showing 404 page for non-existent mirror redirection links
- Move default mirror definition into downloads.py for easy changing
NOTE: this enables mirrors that require a version string to download the current version
of files. Older file versions will *not* be downloadable (that would require parsing the
requested filename to try and find a version). Hey, it's better than no support at all =)