added a guard against recursive calls to exit

original commit: 04791041223649bcbbd1acadd82df376341fa745

collects/mred/exit.ss

@@ -33,6 +33,11 @@
 		 [else (loop (cdr cb-list))])))))
 
     (define -exit
+      (let ([exiting? #f])
+	(lambda ()
+	  (unless exiting?
+	    (dynamic-wind
+	     (lambda () (set! exiting? #t))
 	     (lambda ()
 	       (let/ec k
 		 (when (and (mred:preferences:get-preference 'mred:verify-exit)
@@ -48,8 +53,8 @@
 		   (k #f))
 		 (run-exit-callbacks)
 		 (if (null? exit-callbacks)
-	      (begin (when mred:debug:exit?
-		       (exit))
-		     #t)
-	      #f))))))
+		     (exit)
+		     #f)))
+	     (lambda () (set! exiting? #f)))))))))
+