filter out duplicate date changed events sent by the native control (part of bug 1482773)

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@42207 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/msw/datectrl.h

@@ -60,6 +60,9 @@ public:
 protected:
     virtual wxSize DoGetBestSize() const;
 
+    // the date currently shown by the control, may be invalid
+    wxDateTime m_date;
+
 
     DECLARE_DYNAMIC_CLASS_NO_COPY(wxDatePickerCtrl)
 };