tools: add tiny_ssim

Taken from:
http://lists.mplayerhq.hu/pipermail/mencoder-users/2006-August/003801.html
and
x264
See: [FFmpeg-devel] [PATCH] tools: add tiny_ssim

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
tiny_ssim: Avoid "for(int ..."

This should avoid issues with old compilers

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>
mpegvideo/h264: drop period_since_free

This should not be needed anymore

Signed-off-by: Michael Niedermayer <michaelni@gmx.at>