Intoduce new osgWidget::PdfReader and osgWidget::VncClient front ends to osgWidget,

with new pdf plugin and updated vnc plugin that now support these front ends.

Updated osgpdf and osgvnc examples to new these new interfaces.

include/osgViewer/ViewerEventHandlers

@@ -373,7 +373,7 @@ public:
         _image(image) {}
 
     META_Object(osgViewer, InteractiveImageHandler);
-
+ 
     virtual bool handle(const osgGA::GUIEventAdapter& ea,osgGA::GUIActionAdapter& aa, osg::Object*, osg::NodeVisitor* nv);
 
     virtual bool cull(osg::NodeVisitor* nv, osg::Drawable* drawable, osg::RenderInfo* renderInfo) const;
@@ -389,6 +389,10 @@ protected:
     bool mousePosition(osgViewer::View* view, osg::NodeVisitor* nv, const osgGA::GUIEventAdapter& ea, int& x, int &y) const;
 
     osg::observer_ptr<osg::Image>  _image;
+    bool    _handleKeyboardEvents;
+    bool    _handledOnKeyboardEvents;
+    bool    _handleMouseEvents;
+    bool    _handledOnMouseEvents;
     
 };