gst/gstbus.c: gst_bus_poll may be called from other threads. Handle this nicely by...

gst/gstbus.c: gst_bus_poll may be called from other threads. Handle this nicely by not making poll_data disappear off...

Original commit message from CVS:
* gst/gstbus.c: (gst_bus_set_flushing), (gst_bus_pop),
(gst_bus_peek), (gst_bus_source_dispatch),
(gst_bus_add_watch_full), (poll_handler), (poll_timeout),
(poll_destroy), (poll_destroy_timeout), (gst_bus_poll):
gst_bus_poll may be called from other threads. Handle
this nicely by not making poll_data disappear off the
stack once gst_bus_poll returns.
gst_bus_peek now increments the refcount on the returned
message.