Implement wxCalendarCtrl::SetDateRange() in the native GTK version.

While GTK+ doesn't support imposing ranges for dates selection natively, we
can do it ourselves by preventing the user from selecting any date outside of
the currently valid range.

This allows to use ranges under all platforms and not only in wxCalendarCtrl
itself but in wxDatePickerCtrl as well.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@67987 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/gtk/calctrl.h

@@ -38,15 +38,31 @@ public:
     virtual bool SetDate(const wxDateTime& date);
     virtual wxDateTime GetDate() const;
 
+    virtual bool SetDateRange(const wxDateTime& lowerdate = wxDefaultDateTime,
+                              const wxDateTime& upperdate = wxDefaultDateTime);
+    virtual bool GetDateRange(wxDateTime *lowerdate, wxDateTime *upperdate) const;
+
     virtual bool EnableMonthChange(bool enable = true);
 
     virtual void Mark(size_t day, bool mark);
 
     // implementation
     // --------------
-    wxDateTime m_selectedDate;
+
+    void GTKGenerateEvent(wxEventType type);
 
 private:
+    bool IsInValidRange(const wxDateTime& dt) const;
+
+    // Range of the dates that can be selected by user, either or both may be
+    // invalid to indicate that no corresponding restriction is set.
+    wxDateTime m_validStart,
+               m_validEnd;
+
+    // Last known selected date, may be different from the real selection in
+    // the control while a handler for day-selected is running.
+    wxDateTime m_selectedDate;
+
     DECLARE_DYNAMIC_CLASS(wxGtkCalendarCtrl)
     wxDECLARE_NO_COPY_CLASS(wxGtkCalendarCtrl);
 };