Add wxDropSource::SetIcon for wxGTK to mimic SetCursor on the other ports.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@71349 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/gtk/dnd.h

@@ -81,6 +81,17 @@ public:
 
     virtual ~wxDropSource();
 
+    // set the icon corresponding to given drag result
+    void SetIcon(wxDragResult res, const wxIcon& icon)
+    {
+        if ( res == wxDragCopy )
+            m_iconCopy = icon;
+        else if ( res == wxDragMove )
+            m_iconMove = icon;
+        else
+            m_iconNone = icon;
+    }
+
     // start drag action
     virtual wxDragResult DoDragDrop(int flags = wxDrag_CopyOnly);