* introducing dct248 into the DSP context.

   * introducing dct248 into the DSP context.
   * simple/accurate implementation of dct248
   * DV encoding now supports 2-4-8 DCT
   * DV encoding gets a bit faster (but still miles away
     from what I think it could do)
   * misc. DV codec cleanups

Originally committed as revision 2425 to svn://svn.ffmpeg.org/ffmpeg/trunk