ext/dv/gstdvdemux.c: Handle events in push mode better, can now do non-flushing seeks in push mode as well.

Original commit message from CVS:
* ext/dv/gstdvdemux.c: (gst_dvdemux_handle_sink_event),
(gst_dvdemux_convert_segment), (gst_dvdemux_demux_frame):
Handle events in push mode better, can now do non-flushing
seeks in push mode as well.