check/gst/gstbin.c: Added test to check state change order in bins (can still be made to fail here under heavy disk l...

Original commit message from CVS:
* check/gst/gstbin.c: (test_children_state_change_order_flagged_sink),
(test_children_state_change_order_semi_sink), (gst_bin_suite):
Added test to check state change order in bins (can still be made
to fail here under heavy disk load; bails out with 'Push on pad
fakesink:sink0, but it was not activated in push mode').
* gst/gstbin.c: (gst_bin_class_init), (gst_bin_change_state):
Fix state change order when there is only a semi sink (#316856)
* gst/gstbus.c: (gst_bus_class_init):
Use _class_peek_parent(), not _class_ref(); fix docs to say
'default main context' instead of 'mainloop' where that is
what's meant.
* gst/gstelement.c: (gst_element_commit_state),
(gst_element_set_state):
Fix typos in debug messages