gst/playback/: More fixes, cleaned up playbin, make it use decodebin. Added threaded...

gst/playback/: More fixes, cleaned up playbin, make it use decodebin. Added threaded property to playbin.

Original commit message from CVS:
* gst/playback/gstdecodebin.c: (gst_decode_bin_get_type),
(gst_decode_bin_class_init), (gst_decode_bin_factory_filter),
(compare_ranks), (gst_decode_bin_init), (gst_decode_bin_dispose),
(find_compatibles), (close_pad_link), (try_to_link_1), (new_pad),
(close_link), (type_found), (gst_decode_bin_set_property),
(gst_decode_bin_get_property), (gst_decode_bin_get_event_masks),
(gst_decode_bin_send_event), (gst_decode_bin_get_formats),
(gst_decode_bin_convert), (gst_decode_bin_get_query_types),
(gst_decode_bin_query), (plugin_init):
* gst/playback/gstplaybin.c: (gst_play_bin_get_type),
(gst_play_bin_class_init), (gst_play_bin_init),
(gst_play_bin_dispose), (rebuild_pipeline), (get_audio_element),
(get_video_element), (new_pad), (setup_source),
(gst_play_bin_set_property), (gst_play_bin_get_property),
(gst_play_bin_change_state), (gst_play_bin_add_element),
(gst_play_bin_remove_element), (gst_play_bin_get_event_masks),
(gst_play_bin_send_event), (gst_play_bin_get_formats),
(gst_play_bin_convert), (gst_play_bin_get_query_types),
(gst_play_bin_query), (gst_play_bin_get_clock), (plugin_init):
* gst/playback/test.c: (main):
More fixes, cleaned up playbin, make it use decodebin. Added
threaded property to playbin.