gst/playback/gstplaybin2.c: Code cleanups.

gst/playback/gstplaybin2.c: Code cleanups.

Original commit message from CVS:
* gst/playback/gstplaybin2.c: (gst_play_bin_class_init),
(gst_play_bin_finalize), (gst_play_bin_set_uri),
(gst_play_bin_set_suburi), (gst_play_bin_set_property),
(gst_play_bin_get_property), (pad_removed_cb), (drained_cb),
(autoplug_select_cb), (activate_group), (deactivate_group),
(setup_next_source), (save_current_group),
(gst_play_bin_change_state):
Code cleanups.
Remove next-uri, we can use the uri property just fine.
Fix some crasher.
Unref uridecodebin when switching.
Fix going to READY.
* gst/playback/gstplaysink.c: (gst_play_sink_class_init),
(gst_play_sink_init), (gst_play_sink_dispose),
(gst_play_sink_finalize), (gst_play_sink_vis_unblocked),
(gst_play_sink_vis_blocked), (gst_play_sink_set_video_sink),
(gst_play_sink_set_audio_sink), (gst_play_sink_set_vis_plugin),
(gst_play_sink_set_property), (gst_play_sink_get_property),
(gen_video_chain), (gen_text_element), (gen_audio_chain),
(gen_vis_element), (gst_play_sink_get_mode),
(gst_play_sink_set_mode), (gst_play_sink_set_flags),
(gst_play_sink_get_flags), (gst_play_sink_request_pad),
(gst_play_sink_release_pad), (gst_play_sink_send_event_to_sink),
(gst_play_sink_change_state):
* gst/playback/gstplaysink.h:
Add some locking to make things threadsafe.
* gst/playback/test7.c: (about_to_finish_cb):
Fix test.