This changes filename from "latest" to explicit versioned name.
As official site doesn't provide old tarballs, we use
http://code.google.com/p/live555sourcecontrol/downloads instead.

Note: when updating contrib to new version, need to get checksum from
official site, not from there! Just in case...
Signed-off-by: Rémi Denis-Courmont <remi@remlab.net>