Movable pole drag event triggers double scene redraw
The current implementation of MMovablePoleActor::dragEvent() triggers a double scene redraw. In line 783ff ("Update GUI properties."), setting the property also triggers an unnecessary regeneration of geometry and redraw. This statement needs to be encapsulated in "enableActorUpdates(false); / enableActorUpdates(true);", but doing that breaks correct dragging if mulitple poles are present.