Added wxDC::GetAsBitmap, and implemented wxWindowDC::DoGetAsBitmap on OS X, in order to restore the ability to blit the contents of those DCs.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@42604 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/mac/carbon/dcclient.h

@@ -35,6 +35,7 @@ class WXDLLEXPORT wxWindowDC: public wxDC
   wxWindow *GetWindow() const { return m_window; }
   protected :
     virtual void DoGetSize( int *width, int *height ) const;
+    virtual wxBitmap DoGetAsBitmap() const; 
     wxWindow     *m_window;
 #if wxMAC_USE_CORE_GRAPHICS
 	bool		m_release;