Automated checkin: version bump for firefox 21.0b7 release. DONTBUILD CLOSED TREE a=release

--HG--
branch : GECKO210b7_2013050618_RELBRANCH
Added FIREFOX_21_0b7_RELEASE FIREFOX_21_0b7_BUILD1 tag(s) for changeset 0fe6378ac802. DONTBUILD CLOSED TREE a=release

--HG--
branch : GECKO210b7_2013050618_RELBRANCH