gst/gstmessage.*: Clean up.

gst/gstmessage.*: Clean up.

Original commit message from CVS:
* gst/gstmessage.c: (gst_message_new_custom),
(gst_message_new_eos), (gst_message_new_error),
(gst_message_new_warning), (gst_message_new_tag),
(gst_message_new_state_changed), (gst_message_new_clock_provide),
(gst_message_new_new_clock), (gst_message_new_segment_start),
(gst_message_new_segment_done), (gst_message_parse_state_changed),
(gst_message_parse_clock_provide), (gst_message_parse_new_clock):
* gst/gstmessage.h:
Clean up.
Added clock related messages.

* gst/gstpipeline.c: (gst_pipeline_change_state):
Post message when the clock changed.

* tools/gst-launch.c: (event_loop):
Print new clock.