assert if wxCAL_SEQUENTIAL_MONTH_SELECTION style is changed after creation as this doesn't currently work

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@43529 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/generic/calctrl.h

@@ -155,6 +155,8 @@ public:
     virtual bool Enable(bool enable = true);
     virtual bool Show(bool show = true);
 
+    virtual void SetWindowStyleFlag(long style);
+
     virtual wxVisualAttributes GetDefaultAttributes() const
         { return GetClassDefaultAttributes(GetWindowVariant()); }