fix racket/gui/dynamic and add multi-instance checks

original commit: fa3d9cdf28bdba2643c54025fee1fcc7dab84376

collects/mred/private/wx/common/queue.rkt

@@ -38,6 +38,15 @@
 
          queue-quit-event)
 
+;; ------------------------------------------------------------
+;; This module must be instantiated only once:
+
+(define-mz scheme_register_process_global (_fun _string _pointer -> _pointer))
+(let ([v (scheme_register_process_global "GRacket-support-initialized"
+                                         (cast 1 _scheme _pointer))])
+  (when v
+    (error "cannot start GRacket a second time in the same process")))
+
 ;; ------------------------------------------------------------
 ;; Create a Scheme evt that is ready when a queue is nonempty