* some significant clean-up of the dv_decode_ac (it looks real
     simple now, take a look for yourself).

   * additional optimizations of the decoder. It runs at 55fps now
     on my desktop and it used to be ~45fps.


git-svn-id: file:///var/local/repositories/ffmpeg/trunk@2926 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b