Original commit message from CVS:
* gst/playback/gstplaybin2.c: (gst_play_bin_set_property):
Enable vis setting.
* gst/playback/gstplaysink.c: (gst_play_sink_init),
(gst_play_sink_dispose), (gst_play_sink_vis_unblocked),
(gst_play_sink_vis_blocked), (gst_play_sink_set_vis_plugin),
(gen_vis_chain):
Implement vis switching while playing.