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/GraphicsWindowCarbon.cpp

@@ -485,6 +485,10 @@ struct OSXCarbonWindowingSystemInterface : public osg::GraphicsContext::Windowin
 
 void GraphicsWindowCarbon::init()
 {
+    if (_initialized) return;
+
+    getEventQueue()->setCurrentEventState(osgGA::GUIEventAdapter::getAccumulatedEventState().get());
+
     _windowTitleHeight = 0;
     _closeRequested = false;
     _ownsWindow = false;