instead of our own variable.
* ./modules/audio_filter/converter/a52tospdif.c, ./modules/codec/a52.c: added
<unistd.h>, required for bswap.
* ./modules/demux/mp4/libmp4.c: removed an unneccessary semicolon in a
macro definition.
* ./modules/audio_output/esd.c: first attempt at getting esd to work.
* ./modules/video_output/*: split sdl.so into a video and an audio plugin,
and removed useless subdirectories.
* ./modules/audio_output/sdl.c: compilation fix.