Add render window message for events on render window

Common/vtkCommand.cxx

@@ -71,6 +71,7 @@ static const char *vtkCommandEventStrings[] = {
   "PlaceWidgetEvent",
   "CursorChangedEvent",
   "ExecuteInformationEvent",
+  "RenderWindowMessage",
   NULL
 };
 

Common/vtkCommand.h

@@ -151,6 +151,7 @@ public:
     PlaceWidgetEvent,
     CursorChangedEvent,
     ExecuteInformationEvent,
+    RenderWindowMessage,
     UserEvent = 1000
   };
 //ETX