This one replace horizClassify by a
transpose/(use Vert)/transpose sequence.
This add LowPass and DefFilter for "free".
I also fixed the header in postprocess.c
and special-cased some of the well-aligned
cases (all horiz stuff is well-aligned).

patch by (Romain Dolbeau <dolbeau at irisa dot fr>)

Originally committed as revision 3175 to svn://svn.ffmpeg.org/ffmpeg/trunk