GstBusHandler -> GstBusFunc, return value has the same meaning as any other GSource...

GstBusHandler -> GstBusFunc, return value has the same meaning as any other GSource (FALSE == remove source).

Original commit message from CVS:
* check/gst/gstbin.c: (pop_messages), (GST_START_TEST):
* check/gst/gstbus.c: (message_func_eos), (message_func_app),
(send_messages), (GST_START_TEST), (gstbus_suite):
* check/gst/gstpipeline.c: (GST_START_TEST):
* check/pipelines/cleanup.c: (run_pipeline):
* check/pipelines/simple_launch_lines.c: (run_pipeline),
(GST_START_TEST):
* gst/gstbus.c: (gst_bus_have_pending), (gst_bus_source_prepare),
(gst_bus_source_check), (gst_bus_source_dispatch),
(gst_bus_create_watch), (gst_bus_add_watch_full),
(gst_bus_add_watch), (poll_func), (poll_timeout), (gst_bus_poll):
* gst/gstbus.h:
* tools/gst-launch.c: (event_loop):
* tools/gst-md5sum.c: (event_loop):
GstBusHandler -> GstBusFunc, return value has the same meaning as
any other GSource (FALSE == remove source).
_add_watch() and _add_watch_full() now take a MessageType mask to
only handle specific types of messages.
_poll() returns the GstMessage instead of the message type to avoid
race conditions.
_have_pending() takes a MessageType mask now too.
Added testsuite for multiple bus watches.
Fix testsuites and applications for new bus API.