Log Message:
Set DIST_SUBDIR=Mesa-7.0.4.1 (via MESA_PKGVERSION).

This allows people that already have the older custom Mesa-7.0.4 tarballs
to correctly upgrade Mesa to the standard distributions without having to
know to delete the old sources or get confused by the mismatching distinfo
checkhashes.

Update the paths in the related distinfos for the change.