gst/playback/: Reuse the audio and video bins.

gst/playback/: Reuse the audio and video bins.

Original commit message from CVS:
* gst/playback/gstdecodebin.c: (gst_decode_bin_class_init),
(gst_decode_bin_init), (find_compatibles), (close_pad_link),
(try_to_link_1), (no_more_pads), (close_link), (type_found):
* gst/playback/gstplaybasebin.c: (gst_play_base_bin_class_init),
(unknown_type), (gst_play_base_bin_remove_element),
(gst_play_base_bin_link_stream):
* gst/playback/gstplaybasebin.h:
* gst/playback/gstplaybin.c: (gst_play_bin_init),
(gst_play_bin_set_property), (gen_video_element),
(gen_audio_element), (setup_sinks):
* gst/playback/gststreaminfo.c: (gst_stream_type_get_type),
(gst_stream_info_get_type), (gst_stream_info_class_init),
(gst_stream_info_init), (gst_stream_info_new),
(gst_stream_info_dispose), (stream_info_mute_pad),
(gst_stream_info_set_property), (gst_stream_info_get_property):
* gst/playback/gststreaminfo.h:
Reuse the audio and video bins.
Some internal cleanups in the stream selection code.