2009-03-24  Vincent Untz  <vuntz@gnome.org>

	Rework deeply the code that writes the saved session to desktop files:
	we now properly discard a client when removing it; we also make sure we
	save the current session before we completely remove the previously
	saved session (to be on the safe side).
	Note that we only discard a client when the new saved session doesn't
	use the same discard command: for example, when metacity saves its
	state, it will reuse the same discard command and so we can't discard
	the old metacity client (it would discard the new client).

	* gnome-session/gsm-util.[ch]: (gsm_util_get_empty_tmp_session_dir):
	new function to get a temporary directory where to save the new
	session, while we still keep the previously saved session. It also
	makes sure the directory is empty.
	* gnome-session/gsm-session-save.[ch]: (save_one_client): update to
	make sure we remember the discard command from the client.
	(gsm_session_save): rework to first save the session in the temporary
	directory (and remember the discard commands from the saved clients),
	and then clear the old session. We finish by renaming the temporary
	directory to its final name.
	(gsm_session_clear_one_client): new, to properly clear one client from
	a saved session. We unlink the desktop file, but also run the discard
	command if it's not used by any other client from the newly saved
	session.
	(gsm_session_clear_saved_session): change to clear a saved session in a
	specified directory, and use gsm_session_clear_one_client() instead of
	just unlinking the desktop file. Also add missing g_dir_close().

svn path=/trunk/; revision=5355