Added code for 3 state checkbox.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@27656 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/motif/checkbox.h

@@ -16,8 +16,6 @@
 #pragma interface "checkbox.h"
 #endif
 
-#include "wx/control.h"
-
 // Checkbox item (single checkbox)
 class WXDLLEXPORT wxCheckBox: public wxCheckBoxBase
 {
@@ -54,6 +52,10 @@ private:
         m_evtType = wxEVT_COMMAND_CHECKBOX_CLICKED;
     }
 
+    virtual void DoSet3StateValue(wxCheckBoxState state);
+
+    virtual wxCheckBoxState DoGet3StateValue() const;
+
     // public for the callback
 public:
     // either exEVT_COMMAND_CHECKBOX_CLICKED or ..._TOGGLEBUTTON_CLICKED