adding missing lib libgl1-mesa-dri

without: 
libGL error: failed to load driver: vmwgfx
libGL error: failed to load driver: swrast

platform: ubuntu 13.04
auto merge of #464 : Sicki/servo/patch-2, r=metajack

without: 
libGL error: failed to load driver: vmwgfx
libGL error: failed to load driver: swrast

platform: ubuntu 13.04