vc9data.h to select the behaviour
- modified decode_b_picture_primary_header so that
decode_bi_picture_header is no more required

Fixes:
- modifications for some more using of MpegEncContext
- fixed a bit frame type decoding
- switch from pointers to index for AC tables
- corrected P CBPCY decoding (p_cbpcy += 4)

patch by anonymous

Originally committed as revision 3906 to svn://svn.ffmpeg.org/ffmpeg/trunk