This patch adds the support for INTRA PCM macroblocks in CAVLC and CABAC
mode, the deblocking needed a small modification and so did the
intra4x4_pred_mode prediction.

With this patch, the 5 streams of the conformance suite containing INTRA
PCM macroblocks now decode entirely, 4 are completely corrects, 1 is
incorrect since the first B slice because of deblocking in B slice not
yet implemented.

The code is not optimized for speed, it is not necessary IPCM
macroblocks are rare, but it could be optimized for code size, if
someone want to do this, feel free.

Originally committed as revision 3941 to svn://svn.ffmpeg.org/ffmpeg/trunk