simplified adressing of most mb based arrays (mb_x + mb_y*s->mb_stride) now instead of mb_x + mb_y*mb_width and 1+mb_x + (1+mb_y)*(mb_width+2) and ... mixture
more direct use of the new mb_type stuff instead of codec specific stuff
runtime mb_type debug output h264/h263 variants/mpeg1/2/4
error concealment /resilience for mpeg1/2
various minor optimizations

Originally committed as revision 1746 to svn://svn.ffmpeg.org/ffmpeg/trunk