updating nut demuxer to latest spec

updating nut demuxer to latest spec
no muxing yet
no index yet
no seeking yet
libnuts crcs dont match mine (didnt investigate yet)
samplerate is stored wrong by libnut (demuxer has a workaround)
code is not clean or beautifull yet, but i thought its better to commit early before someone unneccesarily wastes his time duplicating the work
demuxer split from muxer

Originally committed as revision 6966 to svn://svn.ffmpeg.org/ffmpeg/trunk