title: fullcalendar return event end null when allDay is true
body: <p>I don't know if it is a feature or a bug. But the event end value is set to null  if allDay is true.
  This is the function where the event is updated:</p>
  
  <pre><code> change: function (eventModel) {
  
  
                  var currEvId = eventModel.get('_id');
                  var fcEvent = $("#calendar").fullCalendar('clientEvents', currEvId)[0] || {};
                   console.log("end before update : " + fcEvent.end);
  
                  fcEvent.title = alvEventModel.get("title");                 
                  fcEvent.start = new Date(alvEventModel.get("start"));
                  fcEvent.end = new Date(alvEventModel.get("end"));
                  fcEvent.allDay = alvEventModel.get("allDay");  //true or false              
                  this.el.fullCalendar('updateEvent', fcEvent);
  
                  console.log("start: " + fcEvent.start);
                  console.log("end: " + fcEvent.end);      
  
              },
  </code></pre>
  
  <p>The console shows </p>
  
  <pre><code>end before update : 1404896400000
  end after update: null 
  </code></pre>
  
  <p>The fullcalendar property forceEventDuration is setted to true</p>
  
  <pre><code>this.$el.fullCalendar({
                      lang: 'sv',
                      header: {
                          left: 'prev,next, today',
                          center: 'title',
                          right: 'month,agendaWeek,agendaDay',
                          ignoreTimezone: false
                      },
                      forceEventDuration:true,
                      select: this.select,
                      selectable: true,
                      selectHelper: true,
                      editable: true,
  
  
                      disableDragging: true,
                      disableResizing: true,
  
                      aspectRatio: 2.5,
                      height: 600,
                      weekNumbers: true,
                       ...
                      })
  </code></pre>
  
  <p>the the console shows</p>
  
  <pre><code>end before update : 1404864000000
  end after update: 1404813300000 
  </code></pre>
  
  <p>I this case the rendering for the event is one day. Even after updating with allDay to false it continue to show as a one day event until reloading the events from server. 
  I think the standard behavior is for allDay must have a start and end date. But I'm not sure the intentions of declaring the end date as null. May be I missunderstand the beauty of this behavior. I don't know how to use for my goals. I need an end date like other calendars.</p>
  
  <p><a href="http://jsfiddle.net/Mr_Vertigo/k3RZX/1/" rel="noreferrer">http://jsfiddle.net/Mr_Vertigo/k3RZX/1/</a>
  And the version is  v2.0.2</p>