Introduced new GUIEventAdatper singleton for sharing the current state between

multiple GraphicsWindows, this singleton is accessable via GUIEventEvent::getAccumulatedEventState().

Added use of this new singleton in GraphicsWindow* implementations.

Added WindowSizeHandler to osgkeyboard to help with debugging of event state
between windows.

src/osgViewer/GraphicsWindowX11.cpp

@@ -456,6 +456,8 @@ void GraphicsWindowX11::init()
         return;
     }
     
+    getEventQueue()->setCurrentEventState(osgGA::GUIEventAdapter::getAccumulatedEventState().get());
+    
     WindowData* inheritedWindowData =  dynamic_cast<WindowData*>(_traits->inheritedWindowData.get());
 
     _display = XOpenDisplay(_traits->displayName().c_str());