targets/xorg: lts-saucy will disappear soon, use lts-trusty

Tested in `2014-07-11_10-20-09_drinkcat_chroagh_x11-test.tmp-lts-trusty-fix-jessie-sid_35` (together with `fix-jessie-sid-mesa`), matrix here: http://drinkcat.github.io/chroagh/2014-07-11_10-20-09_drinkcat_chroagh_x11-test.tmp-lts-trusty-fix-jessie-sid_35.html .