* code with new PAVGB for MMX only CPU splited into separate file
  and being compiled in the same way as _avg.h
* PAVG_MMX macros accept also output parameter
* implemented faster put_pixels_xy2, but it has slightly smaller precission.
  But there is not visible difference in the image quality - might be eventualy
  easily switched back (#if 0 #endif)- please check

Originally committed as revision 624 to svn://svn.ffmpeg.org/ffmpeg/trunk
