Prevent event generation in wxGtkCalendarCtrl::SetDate().

Block not only gtk_day_selected_callback() but also gtk_month_changed_callback()
as we don't want wxEVT_CALENDAR_PAGE_CHANGED generated neither when calling
SetDate().

This fixes partial resetting of the just set value in wxDatePickerCtrl as
calling SetDate() there resulted in the date being reset from inside it and
the behaviour of the control was clearly wrong as could be seen in the widgets
sample.

Closes #13073.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@67293 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775