Fixed PR 6499 (utrace probe crash).

Fixed PR 6499 (utrace probe crash).
2008-05-16  David Smith  <dsmith@redhat.com>

	PR 6499.
	* task_finder.c (stap_register_task_finder_target): Added error
	check.
	(__stp_utrace_task_finder_report_clone): Ditto.
	(stap_utrace_detach_ops): Uses do_each_thread/while_each_thread
	instead of for_each_process (which only iterated among process
	group leaders instead of all threads).
	(stap_start_task_finder): Ditto.