Fixes:
- i/p/b_decode_mbs functions now checks the proper values (from
bitplane). I didn't find it very clear, but it seems "raw" = "to read at
the MB layer". I used a structure, but we could spare that indirection and
add a flag in the VC9Context for each array.
- Properly decode (or so I think) the CBPCY (as it is predicted)
- many more things
patch by anonymous

Originally committed as revision 3882 to svn://svn.ffmpeg.org/ffmpeg/trunk
