Adds a diff_pixels_unaligned()
Fixes: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=872503
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>
(cherry picked from commit bc488ec28aec4bc91ba47283c49c9f7f25696eaa)
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>