cabac bytestream optimization from x264

Originally committed as revision 8776 to svn://svn.ffmpeg.org/ffmpeg/trunk

doc/TODO

@@ -89,3 +89,4 @@ unassigned TODO: (unordered)
 - extract PES packetizer from PS muxer and use it for new TS muxer
 - implement automatic AVBistreamFilter activation
 - port libavformat/sgi.c (now removed) to new image format API
+- make cabac encoder use bytestream (see http://trac.videolan.org/x264/changeset/?format=diff&new=651)