xbmc: update to xbmc-13.alpha-df91888

Signed-off-by: Stephan Raue <stephan@openelec.tv>
ffmpeg: add upstream patch

Signed-off-by: Stephan Raue <stephan@openelec.tv>
mysql: build with system ssl and zlib support

Signed-off-by: Stephan Raue <stephan@openelec.tv>