Log Message:
update to 0.10.21
changes:
-shapewipe: moved from -bad to -good
-videmux: push mode seeking support
-jitterbuffer: new buffering modes: low/high watermark buffering,
 rtp timestamps
-matroskademux: subtitle stream improvements
-multipartdemux: improve header mime-type parsing
-v4l2sink: change rank to NONE so we don't try to autoplug it
-misc fixes