gst/qtdemux/qtdemux.*: Fix seeking for quicktime files. Could still use some more love and sophistication.

Original commit message from CVS:
* gst/qtdemux/qtdemux.c: (gst_qtdemux_init),
(gst_qtdemux_send_event), (gst_qtdemux_handle_src_event),
(gst_qtdemux_change_state), (gst_qtdemux_loop_header):
* gst/qtdemux/qtdemux.h:
Fix seeking for quicktime files. Could still use some more
love and sophistication.