closes #1643

Solve #1643 by forcing an update AFTER a refresh.
This because our wxwidget loop event is not in a separate thread and we need to activate it manually everytime something needs to be changed on the screen. And the loop needs to be convinced that a widget (and the plot is a widget) IS not up-to-date.
In contradistinction with X11 where the server loops independently from the program.

Author: GillesDuvert

src/gdlwxstream.cpp

@@ -127,7 +127,7 @@ void GDLWXStream::Update()
 {
   if (this->valid && container != NULL) {
     container->Refresh();
-	  flush(); //needed otherwise synchro is bad see #1643
+    container->Update(); //solve 1643
     GDLWidget::CallWXEventLoop();
   }
 }