gst/flv/: Get an approximate duration of the file by looking at the timestamp of...

gst/flv/: Get an approximate duration of the file by looking at the timestamp of the last tag in pull mode. If we get...

Original commit message from CVS:
* gst/flv/gstflvdemux.c: (gst_flv_demux_loop):
* gst/flv/gstflvparse.c: (gst_flv_parse_tag_timestamp):
* gst/flv/gstflvparse.h:
Get an approximate duration of the file by looking at the timestamp
of the last tag in pull mode. If we get (maybe better) duration from
metadata later we'll use that instead.