3dnow version of the Horizontal & Vertical Lowpass filters
mmx version of the Horizontal Default filter
mmx2 & C versions of a simple filter described in a paper from ramkishor & karan
added mode flags & quality2mode function


git-svn-id: file:///var/local/repositories/ffmpeg/trunk@152 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b