gst/playback/: Some playbin cleanups mostly refcounting sloppyness.

gst/playback/: Some playbin cleanups mostly refcounting sloppyness.

Original commit message from CVS:
* gst/playback/gstdecodebin.c: (gst_decode_bin_init),
(gst_decode_bin_dispose), (try_to_link_1), (get_our_ghost_pad),
(remove_element_chain), (no_more_pads), (unlinked), (close_link),
(type_found):
* gst/playback/gstplaybasebin.c: (gst_play_base_bin_dispose),
(group_destroy), (group_commit), (queue_overrun),
(gen_preroll_element), (no_more_pads), (preroll_unlinked),
(mute_stream), (new_decoded_pad), (setup_substreams),
(setup_source), (mute_group_type), (set_active_source),
(gst_play_base_bin_change_state):
* gst/playback/gstplaybin.c: (gst_play_bin_dispose),
(gen_video_element), (gen_text_element), (gen_audio_element),
(gen_vis_element), (remove_sinks), (add_sink), (setup_sinks):
* gst/playback/gststreaminfo.c: (gst_stream_info_new),
(gst_stream_info_dispose), (gst_stream_info_set_mute):
* gst/playback/gststreamselector.c: (gst_stream_selector_chain):
Some playbin cleanups mostly refcounting sloppyness.