Ensure that the clossing segment is generated correctly and being
properly pushed.
Added some GST_DEBUG to check it.
Ensure that last_stop is updated in stream time.
Calculate duration as delta of PTS as it seems more correct than delta
of SCR in some clips that I tested.
Original commit message from CVS:
* gst/mpegdemux/gstmpegdemux.c: (gst_flups_demux_send_data):
* gst/mpegdemux/gstmpegdemux.h:
The position member in the newsegment event corresponds to the
stream_time of the segment start position.