added rosdep for yasm

also, I notice that you have to separately go to 3rdparty and make--can ffmpeg and libvpx be wrapped in ros packages so that this is not necessary?  Or is the strategy here that we're hoping the apt-gettable versions will catch up soon to what we need?  (If that's the case, can we at least add something to CMakeLists to make it automatically go to 3rdparty and run make when you use rosmake?)