Original commit message from CVS:
* gst/gstbin.c: (bin_replace_message), (gst_bin_add_func),
(gst_bin_change_state_func), (bin_query_min_max_init),
(bin_query_latency_fold), (bin_query_latency_done),
(gst_bin_query):
Improve debug info.
Implement latency query.