Add a filter to act as a buffer between filters which may output multiple

Add a filter to act as a buffer between filters which may output multiple
frames for a single call to request_filter(), and a following filter which
assumes it will only receive one frame per call.

Commited in SoC by Bobby Bingham on 2007-08-18 03:17:52

Originally committed as revision 12016 to svn://svn.ffmpeg.org/ffmpeg/trunk