Fix cdg reference and buffer_hints value:reference must be 3 because both "fields" are used as reference,and buffer_hints must include readable since we might memcpy from the old frame.
Originally committed as revision 20923 to svn://svn.ffmpeg.org/ffmpeg/trunk
CD+G demuxer and decoder
Patch by Michael Tison (gmail address: blackspike@....)
Originally committed as revision 20890 to svn://svn.ffmpeg.org/ffmpeg/trunk