gst/playback/gstplaybin.c: Don't reference all sinks, but only the video- and audiosinks.

gst/playback/gstplaybin.c: Don't reference all sinks, but only the video- and audiosinks.

Original commit message from CVS:
* gst/playback/gstplaybin.c: (gen_video_element),
(gen_audio_element), (setup_sinks), (gst_play_bin_change_state):
Don't reference all sinks, but only the video- and audiosinks.
The vis. element should be disposed when we're done with it.
We don't have any reason to keep it around. This fixes warnings
when reusing playbin for playing multiple audio files with
vis. enabled. Also release audio device on pause - idea stolen
from Rhythmbox.