require file that defines constant used in controller, fixes #763

app/controllers/calendar/schedule.php

@@ -15,6 +15,10 @@
  * @category    Stud.IP
  * @since      2.0
  */
+
+// Needs to be required due to the use of constants
+require_once 'lib/classes/calendar/CalendarScheduleModel.php';
+
 class Calendar_ScheduleController extends AuthenticatedController
 {