gst/gstbus.*: Added async-message and sync-message signals to the bus.

gst/gstbus.*: Added async-message and sync-message signals to the bus.

Original commit message from CVS:
* gst/gstbus.c: (marshal_VOID__MINIOBJECT), (gst_bus_class_init),
(gst_bus_post), (poll_func), (gst_bus_async_signal_func),
(gst_bus_sync_signal_handler):
* gst/gstbus.h:
Added async-message and sync-message signals to the bus.
Added helper BusFunc to emit signals for all posted messages.

* gst/gstmessage.c: (gst_message_type_get_name),
(gst_message_type_to_quark), (gst_message_get_type):
* gst/gstmessage.h:
Register quarks for message names.