title: FullCalendar does not unselect previous selection
body: <p>I've been working with FullCalendar lately for a reservation system.
  The problem is that whenever I select a time range it all adds to the eventData object. What I am trying to do is select one time range only. </p>
  
  <p>When I click the <code>$('#btn-reserve')</code> button it should render the event on the calendar. </p>
  
  <p>What's happening is that even my previous selections are getting rendered on the calendar. I only want to render the last selection I made.</p>
  
  <p>here is my code</p>
  
  <pre><code>$('.calendar').fullCalendar({
      selectable: true,
      select: function(start, end) {
              $('#end_time').val(end);
              $('#start_time').val(start);
              $('#newScheduleModal').modal({
                  show : true,
                  backdrop: 'static',
                  keyboard: false
              });
  
              $('#btn-reserve').click(function(){
                      eventData = {
                          title: 'Lesson Schedule',
                          start: start,
                          end: end
                      };
                      $('.calendar').fullCalendar('renderEvent', eventData, true); // stick? = true
                      $('#newScheduleModal').modal('hide');
              });
  
              $('#btn-cancel-reserve').click(function(){
                  $('.calendar').fullCalendar('unselect');
                  eventData = {};
              })
      },
  
  })
  </code></pre>