Fix for avresample and to get travis working again

./configure --with-avresample will use avresample instead of swresample
ffmpeg has both, but libav only has avresample

Also got travis working, it kinda sucks at the moment, it builds ffmpeg from source... but it works!
The version of ffmpeg in ubuntu precise is pretty old, 0.10. The version I've been using is 1.2 (from homebrew). Porting the code to that early version would require a lot of work.