check/: Moved sinks2 testcode in sinks check.

check/: Moved sinks2 testcode in sinks check.

Original commit message from CVS:
* check/Makefile.am:
* check/states/sinks.c: (GST_START_TEST), (gst_object_suite):
* check/states/sinks2.c:
Moved sinks2 testcode in sinks check.

* gst/gstbin.c: (gst_bin_provide_clock_func), (gst_bin_add_func),
(gst_bin_remove_func), (gst_bin_recalc_state),
(gst_bin_change_state_func), (bin_bus_handler):
Fix potential race condition when _get_state() iterated over an
ASYNC element right before it posted a state completion.

* gst/gstclock.h:
Do proper cast here.

* gst/gstevent.c: (gst_event_new_newsegment),
(gst_event_parse_newsegment):
A playback rate of 0.0 is not allowed.