have core ask windowport if suspend is ok

PORTS: Please make sure I've done the right thing for/to your code.
This patch adds a new winproc that lets the window port approve or cancel
the suspend request - this should take care of the Mac Qt lockup issue.
In addition, Unix suspend is restricted to accounts that can use the shell
if SYSCF is defined.

sys/mac/macwin.c

@@ -3293,6 +3293,7 @@ struct window_procs mac_procs = {
 	0, //    mac_end_screen,
 	genl_outrip,
 	genl_preference_update,
+	genl_can_suspend_no,
 };
 
 /*macwin.c*/