fix bug with calling dynamically added event-source callbacks
fix bug with calling dynamically added event-source callbacks

arshaw/fullcalendar,oleg-babintsev/fullcalendar,arshaw/fullcalendar,oleg-babintsev/fullcalendar,oleg-babintsev/fullcalendar,fullcalendar/fullcalendar,fullcalendar/fullcalendar,arshaw/fullcalendar,fullcalendar/fullcalendar,arshaw/fullcalendar,fullcalendar/fullcalendar