Small fix to message-handler invocation

os.rkt

@@ -227,9 +227,9 @@
      [((apply-getter (vm-vtable state))
        (message-handler-pattern (car message-handlers))
        message)
-      (perform-transition ((message-handler-k (car message-handlers))
-			   (subscription-state sub))
-			  state)]
+      (define trapk (message-handler-k (car message-handlers)))
+      (define interruptk (trapk message))
+      (perform-transition (interruptk (subscription-state sub)) state)]
      [else
       (search-handlers (cdr message-handlers))])))