* 5zosinte.ads (null_pthread): new constant.

	* 5ztaprop.adb:
	(Initialize_TCB): Initialize thread ID to null, to be able to verify
	 later that this field has been set.
	(Finalize_TCB): ditto.
	(Suspend_Task): Verify that the thread ID is not null before using it.
	(Resume_Task): ditto.

	* s-tasdeb.adb:
	(Resume_All_Tasks): Lock the tasks list before using it.
	(Suspend_All_Tasks): ditto.

From-SVN: r46548