check/gst/gstbin.c: add test for state change message on a bin

check/gst/gstbin.c: add test for state change message on a bin

Original commit message from CVS:

* check/gst/gstbin.c: (START_TEST), (gst_bin_suite):
add test for state change message on a bin
* check/gst/gstelement.c: (START_TEST), (gst_element_suite):
add another test
* gst/gstbin.c: (gst_bin_init):
* gst/gstbus.c: (gst_bus_init), (gst_bus_post):
* gst/gstelement.c: (gst_element_post_message),
(gst_element_set_state):
* gst/gstelementfactory.c: (gst_element_factory_create):
* gst/gstmessage.c: (gst_message_new):
* gst/gstscheduler.c:
various debugging additions and cleanups