- renaming the AC coding set variable names to more meaningful ones

- removed old MB decoding functions, and moved around macros to be used in
the previously unused code, which match better msmpeg4.c/whole MPV
framework
- cleaned (not yet functionnal, lots missing) DC prediction
- trying to pass the proper coded status to block decoder
patch by anonymous

Originally committed as revision 3973 to svn://svn.ffmpeg.org/ffmpeg/trunk