nut (de)muxer update

 conform to latest spec
 remove get/put_s() not needed anymore
 update_packetheader() fixed (wasnt always working)
 store/load extradata & aspect ratio
 memleak fix
 dont use vorbis by default yet
 use frame_size from the codec instead of hardcoding it in the source

Originally committed as revision 2951 to svn://svn.ffmpeg.org/ffmpeg/trunk