added wxWindow::IsDoubleBuffered() and improve wxBufferedDC (patch 1565330)

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@41810 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/gtk1/dc.h

@@ -66,6 +66,8 @@ public:
 
     virtual void ComputeScaleAndOrigin();
 
+    virtual GdkWindow* GetGDKWindow() const { return NULL; }
+
     wxCoord XDEV2LOG(wxCoord x) const
     {
         wxCoord new_x = x - m_deviceOriginX;

include/wx/gtk1/dcclient.h

@@ -100,6 +100,8 @@ public:
     virtual wxSize GetPPI() const;
     virtual int GetDepth() const;
 
+    virtual GdkWindow* GetGDKWindow() const { return m_window; }
+
     // implementation
     // --------------
 

include/wx/gtk1/window.h

@@ -108,6 +108,8 @@ public:
     virtual void SetDropTarget( wxDropTarget *dropTarget );
 #endif // wxUSE_DRAG_AND_DROP
 
+    virtual bool IsDoubleBuffered() const { return false; }
+
     // implementation
     // --------------