Make messages future proof. state-change gets a flag if it was a message comming from the streaming thread.

Original commit message from CVS:
* check/gst/gstbin.c: (GST_START_TEST):
* check/gst/gstmessage.c: (GST_START_TEST):
* check/gst/gstpipeline.c: (GST_START_TEST), (message_received):
* gst/gstbin.c: (bin_bus_handler):
* gst/gstelement.c: (gst_element_commit_state),
(gst_element_lost_state):
* gst/gstmessage.c: (gst_message_new_state_changed),
(gst_message_new_segment_start), (gst_message_new_segment_done),
(gst_message_new_duration), (gst_message_parse_state_changed),
(gst_message_parse_segment_start),
(gst_message_parse_segment_done), (gst_message_parse_duration):
* gst/gstmessage.h:
* tools/gst-launch.c: (event_loop):
Make messages future proof.
state-change gets a flag if it was a message comming from the
streaming thread.
segment-start/stop can also be specified in other formats.
A message to notify an app that a pipeline changed playback
duration.
Also fix a GstMessage leak in -launch