Original commit message from CVS:
* gst/adder/gstadder.c: (gst_adder_query_duration),
(forward_event_func), (forward_event), (gst_adder_src_event):
Fix adder seeking.
Make query/seeking code threadsafe.
* tests/check/Makefile.am:
* tests/check/elements/adder.c: (test_event_message_received),
(GST_START_TEST), (test_play_twice_message_received):
Fix adder test case.