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.

include/extern.h

@@ -2574,6 +2574,8 @@ E boolean FDECL(mwelded, (struct obj *));
 /* ### windows.c ### */
 
 E void FDECL(choose_windows, (const char *));
+E boolean NDECL(genl_can_suspend_no);
+E boolean NDECL(genl_can_suspend_yes);
 E char FDECL(genl_message_menu, (CHAR_P,int,const char *));
 E void FDECL(genl_preference_update, (const char *));
 E char *FDECL(genl_getmsghistory, (BOOLEAN_P));

include/winprocs.h

@@ -80,6 +80,7 @@ struct window_procs {
     void FDECL((*win_status_threshold), (int,int,anything,int,int,int));
 # endif
 #endif
+    boolean NDECL((*win_can_suspend));
 };
 
 extern