clarify

git-svn-id: file:///var/local/repositories/ffmpeg/trunk@10449 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b

doc/snow.txt

@@ -362,8 +362,8 @@ diagonal not containing the fullpel point
 
 
 the remaining points shall be bilinearly interpolated from the
-up to 4 surrounding halfpel points, again rounding should be to nearest and
-halfway values rounded up
+up to 4 surrounding halfpel and fullpel points, again rounding should be to
+nearest and halfway values rounded up
 
 compliant snow decoders MUST support 1-1/8 pel luma and 1/2-1/16 pel chroma
 interpolation at least