Add an accessor to get the current drop source from window.mm so that we can implement GiveFeedback support, and also move a couple functions that check the current drop source into common DND OS X code as a result.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@63412 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/osx/dnd.h

@@ -96,6 +96,7 @@ public:
     wxWindow*     GetWindow() { return m_window ; }
     void SetCurrentDragPasteboard( void* dragpasteboard ) { m_currentDragPasteboard = dragpasteboard ; }
     bool MacInstallDefaultCursor(wxDragResult effect) ;
+    static wxDropSource* GetCurrentDropSource();
   protected :
 
     wxWindow        *m_window;