skip motion estimation and encoding of non direct-0,0 MBs if the next MB is skiped (mpeg4 doesnt allow such MBs and in the past we did ME and encoding until at the end we droped them, so this should be faster though i didnt benchmark it, benchmark welcome) 


git-svn-id: file:///var/local/repositories/ffmpeg/trunk@7343 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b