gst/gstbin.*: Immediatly commit the toplevel bin state when receiving an async-done message. This enables us to avoid...

Original commit message from CVS:
* gst/gstbin.c: (gst_bin_init), (gst_bin_add_func),
(gst_bin_remove_func), (gst_bin_get_state_func),
(gst_bin_element_set_state), (gst_bin_continue_func),
(bin_push_state_continue), (bin_handle_async_start),
(bin_handle_async_done), (gst_bin_handle_message_func):
* gst/gstbin.h:
Immediatly commit the toplevel bin state when receiving an async-done
message. This enables us to avoid spawning a thread to commit the state
in some common cases and it also avoids some races.
Avoid spawning a state thread when adding/removing async elements to a
toplevel bin. Instead we immediatly update the bin state.
Get rid of iterating all the children when getting the state in the bin
because it is now always up-to-date.
Fix bug where locked elements would always return _SUCCESS even it they
returned NO_PREROLL before being locked.
Fix the order of the state_change, async-start/done messages that was
sometimes incorrect.
Mark the state_dirty field as deprecated, we don't need it anymore as we
are always up-to-date.
* gst/gstelement.c: (gst_element_get_state_func),
(gst_element_continue_state):
Small debug inprovements.
Return the previous element state return when nothing is pending instead
of blindly returning SUCCESS.
* tests/check/generic/sinks.c: (GST_START_TEST), (pad_blocked_cb),
(gst_sinks_suite):
Add a whole bunch of new testcases.