Recognize the buddy text control as part of wxSpinCtrl.

This allows the code in wxWindowMSW::HandleCtlColor() to find the correct
control when handling the messages from the buddy control and hence setting
the colours for wxSpinCtrl works after this change.

Closes #1691.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@61845 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/msw/spinctrl.h

@@ -90,6 +90,9 @@ public:
     // process a WM_COMMAND generated by the buddy text control
     bool ProcessTextCommand(WXWORD cmd, WXWORD id);
 
+    // recognize buddy window as part of this control at wx level
+    virtual bool ContainsHWND(WXHWND hWnd) const { return hWnd == m_hwndBuddy; }
+
 protected:
     virtual void DoGetPosition(int *x, int *y) const;
     virtual void DoMoveWindow(int x, int y, int width, int height);