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
106f0d98f8