FLAC: add 24-bit encoding.

Works via a dedicated encoder: "FLAC (24-bit)", "ffflac24".

Users who prefer 16-bit can use the previous FLAC encoder: "FLAC (ffmpeg)", "ffflac".



git-svn-id: svn://svn.handbrake.fr/HandBrake/trunk@5134 b64f7644-9d1e-0410-96f1-a4d463321fa5