Add wxTLW::SetModified to allow apps to set the TLW's dirty state. On Mac this gives us the dot in the close button, not implemented elsewhere yet.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@62796 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/osx/toplevel.h

@@ -75,6 +75,9 @@ public:
     virtual void SetTitle( const wxString& title);
     virtual wxString GetTitle() const;
 
+    virtual void SetModified(bool modified);
+    virtual bool GetModified() const;
+
 protected:
     // common part of all ctors
     void Init();