title: RefetchEvents fullcalendar from single event source
body: <p>Am working in fullcalandar jquery plugin,but now i stuck with refetching calendar.
  I have two event sources , and i have made custom refresh button on calendar headar. I want to do refetch events only from second event source whenever user hits refresh button.</p>
  
  <p>Is there any way to pass paramater in fullcalendar refetchEvents and do refetch from single event source.</p>
  
  <pre><code>events: function(start, end, timezone,callback) {
              $.ajax({
                  url:  //FIRST EVENT SOURCE
                  dataType: 'json',
  
                  success: function(response) {
                      //attaching the response to the calendar
            }
  
            $.ajax({
                  url:  // SECOND EVENT SOURCE
                  dataType: 'json',
  
                  success: function(response) {
                      //attaching response to calendar
                   }
               });
         }
  </code></pre>
  
  <p>Whenever user clicks on custom Refresh button , am doing <code>$("#calendar").fullcalendar('refetchEvents');</code> -- this will refetch whole calendar (first + second event source)</p>
  
  <p>What i expect to do is , i want to do refetch only for second event source.</p>