gst/base/gstbasesink.c: Prepare for more accurate position reporting and query handling.

gst/base/gstbasesink.c: Prepare for more accurate position reporting and query handling.

Original commit message from CVS:
* gst/base/gstbasesink.c: (gst_base_sink_class_init),
(gst_base_sink_send_event), (gst_base_sink_peer_query),
(gst_base_sink_query):
Prepare for more accurate position reporting and query
handling.

* gst/gstelement.c: (gst_element_send_event),
(gst_element_set_state):
Add some comment.