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
this way it works on 64-bit archs too.
Patch by Jindřich Makovička ($lastname without last letter and háček, gmail)
Originally committed as revision 22093 to svn://svn.ffmpeg.org/ffmpeg/trunk
Reviewed and corrected by myself because there were no other volunteers in the
last weeks.
Originally committed as revision 21531 to svn://svn.ffmpeg.org/ffmpeg/trunk