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/amiga/winami.c

@@ -93,6 +93,7 @@ struct window_procs amii_procs =
     genl_status_threshold,
 # endif
 #endif
+    genl_can_suspend_yes,
 };
 
 /* The view window layout uses the same function names so we can use
@@ -164,6 +165,7 @@ struct window_procs amiv_procs =
     genl_status_threshold,
 # endif
 #endif
+    genl_can_suspend_yes,
 };
 
 unsigned short amii_initmap[ AMII_MAXCOLORS ];