gst/realmedia/rmdemux.*: Remember first timestamp encountered in stream and re-timest...

gst/realmedia/rmdemux.*: Remember first timestamp encountered in stream and re-timestamp stream to start from zero (f...

Original commit message from CVS:
* gst/realmedia/rmdemux.c: (gst_rmdemux_init),
(gst_rmdemux_sink_event), (gst_rmdemux_perform_seek),
(gst_rmdemux_reset), (gst_rmdemux_chain), (gst_rmdemux_add_stream),
(gst_rmdemux_parse_packet):
* gst/realmedia/rmdemux.h:
Remember first timestamp encountered in stream and re-timestamp
stream to start from zero (fixes #397219); only send one newsegment
event, not two; when seeking, send newsegment events from the
streaming thread and not from the seeking thread.