gst/xingheader/gstxingmux.c: Choose smallest possible frame size for the Xing header...

gst/xingheader/gstxingmux.c: Choose smallest possible frame size for the Xing header, properly set the timestamp, dur...

Original commit message from CVS:
* gst/xingheader/gstxingmux.c: (has_xing_header),
(generate_xing_header), (gst_xing_mux_chain),
(gst_xing_mux_sink_event):
Choose smallest possible frame size for the Xing header, properly
set the timestamp, duration and offset on the outgoing buffers,
only send NEWSEGMENT events in BYTE format downstream and also
drop VBRI headers if already existing.