gst/realmedia/rmdemux.*: Keep track of the first timestamp of the stream and add...

gst/realmedia/rmdemux.*: Keep track of the first timestamp of the stream and add this to the outgoing buffer timestam...

Original commit message from CVS:
* gst/realmedia/rmdemux.c: (gst_rmdemux_init),
(find_seek_offset_time), (gst_rmdemux_reset), (gst_rmdemux_chain),
(gst_rmdemux_parse_mdpr), (gst_rmdemux_descramble_cook_audio),
(gst_rmdemux_descramble_dnet_audio),
(gst_rmdemux_parse_video_packet), (gst_rmdemux_parse_audio_packet):
* gst/realmedia/rmdemux.h:
Keep track of the first timestamp of the stream and add this to the
outgoing buffer timestamps so that we can handle live streams.
Set discont flag on the first buffers and after a seek.