Add missing virtual dtor for pure virtual bases.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/branches/WX_2_4_BRANCH@34731 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/datetime.h

@@ -1296,6 +1296,9 @@ class WXDLLEXPORT wxDateTimeHolidayAuthority
 {
 friend class wxDateTimeHolidaysModule;
 public:
+    // virtual dtor for pure virtual base.
+    virtual ~wxDateTimeHolidayAuthority() {}
+
     // returns TRUE if the given date is a holiday
     static bool IsHoliday(const wxDateTime& dt);