gst/playback/: Better error recovery. Added configurable preroll queue size. Faster detection of no-more-pads.

Original commit message from CVS:
* gst/playback/gstdecodebin.c: (gst_decode_bin_get_type),
(gst_decode_bin_class_init), (gst_decode_bin_is_dynamic),
(gst_decode_bin_factory_filter), (compare_ranks), (print_feature),
(gst_decode_bin_init), (gst_decode_bin_dispose),
(find_compatibles), (close_pad_link), (try_to_link_1), (new_pad),
(no_more_pads), (close_link), (type_found),
(gst_decode_bin_set_property), (gst_decode_bin_get_property),
(gst_decode_bin_change_state), (plugin_init):
* gst/playback/gstplaybasebin.c: (gst_play_base_bin_get_type),
(gst_play_base_bin_class_init), (gst_play_base_bin_init),
(gst_play_base_bin_dispose), (queue_overrun),
(gen_preroll_element), (remove_prerolls), (unknown_type),
(no_more_pads), (new_stream), (setup_source),
(gst_play_base_bin_set_property), (gst_play_base_bin_get_property),
(play_base_eos), (gst_play_base_bin_change_state),
(gst_play_base_bin_add_element),
(gst_play_base_bin_remove_element),
(gst_play_base_bin_mute_stream), (gst_play_base_bin_link_stream),
(gst_play_base_bin_unlink_stream),
(gst_play_base_bin_get_streaminfo):
* gst/playback/gstplaybasebin.h:
Better error recovery. Added configurable preroll queue size. Faster
detection of no-more-pads.