Revert peter's commit to remove cdevsw_add() - it was a bit premature

since things fail to function properly without it (pty allocation becomes
somewhat haphazard).

sys/kern/tty_pty.c

@@ -813,6 +813,8 @@ static void
 ptc_drvinit(unused)
 	void *unused;
 {
+	cdevsw_add(&pts_cdevsw);
+	cdevsw_add(&ptc_cdevsw);
 	/* XXX: Gross hack for DEVFS */
 	ptyinit(0);
 }