ext/mythtv/gstmythtvsrc.c: Correctly set duration to get a more correct seek bar...

ext/mythtv/gstmythtvsrc.c: Correctly set duration to get a more correct seek bar in totem.

Original commit message from CVS:
Patch by: Bastien Nocera <hadess at hadess dot net>
* ext/mythtv/gstmythtvsrc.c: (gst_mythtv_src_class_init),
(gst_mythtv_src_init), (gst_mythtv_src_clear),
(do_read_request_response), (gst_mythtv_src_create),
(gst_mythtv_src_start):
Correctly set duration to get a more correct seek bar in totem.
Disable query and event functions as they don't work and do some
smaller cleanup.
Fixes bug #533736.