Original commit message from CVS:
2008-11-04  Andy Wingo  <wingo@pobox.com>

Add sequence numbers to events and messages. See #559250.

* gst/gstutils.c (gst_util_seqnum_next, gst_util_seqnum_compare):
New functions.

* gst/gstevent.h:
* gst/gstevent.c (_gst_event_copy, gst_event_new): Initialize new
events with a new sequence number, and copy it when copying.
(gst_event_get_seqnum, gst_event_set_seqnum): Accessors for an
event's sequence number.

* gst/gstmessage.h:
* gst/gstmessage.c (_gst_message_copy, gst_message_new_custom):
(gst_event_get_seqnum, gst_event_set_seqnum): As with events, so
with messages.

* docs/gst/gstreamer-sections.txt: Add new functions to the docs.