This moves the DWT functions from snow.c and dsputil.c to a file of
their own. A new struct, DWTContext, holds the function pointers
previously part of DSPContext.
Originally committed as revision 22522 to svn://svn.ffmpeg.org/ffmpeg/trunk
It contains optimizations that are not specific to i386 and
libavutil uses this naming scheme already.
Originally committed as revision 16270 to svn://svn.ffmpeg.org/ffmpeg/trunk