version string: add copyright line to version string

Show the copyright when running `ffmpeg -version'. This is useful for
end users trying to determine whether they are using FFmpeg or Libav.

Signed-off-by: Simon Thelen <ffmpeg@c-14.de>
swscale/input: fix harmless integer overflow

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