media-plugins/live: Add support for gentoo-prefix to my portage-mutilib hack to live-2010.04.09.

(Portage version: 2.2.01.16626-prefix/hg/Linux x86_64, RepoMan options: --force, unsigned Manifest commit)

Bumped to live-2010.04.09, attempting to follow changes for the corresponding bump in portage. Need for bump reported by geos_one.
(Portage version: 2.2_rc67-r8/hg/Linux x86_64)
(Signed Manifest commit)