Patch (GSoC qualfication task) by Zhentan Feng spyfeng gmail com, see
"[FFmpeg-devel] Add waveformat extensible support in wav muxer (SoC
qualification task)" thread on mailinglist.



git-svn-id: file:///var/local/repositories/ffmpeg/trunk@18372 9553f0bf-9b14-0410-a0b8-cfaf0461ba5b