title: How to check value already exist for a day in fullCalendar
body: <p>I'm making a calednar where people can click and book the diffrent days.</p>
  
  <p>The event data that are added to the calendar looks like this:</p>
  
  <pre><code>var myEvent = {
      user_id: 2345,
      title: 'this is a title',
      allDay: true,
      start:  date.format(),
      end: date.format()
  };
  </code></pre>
  
  <p>When its added i want to check if the user_id exist so user dont add event again.</p>
  
  <p>I'm using the <code>dayClick</code> event and the code looks like this:</p>
  
  <pre><code>dayClick: function(date, jsEvent, view) {
  
      var myEvent = {
          user_id: userid,
          title: title,
          allDay: true,
          start:  date.format(),
          end: date.format()
      };
  
      var allEvents = allEvents = $('.calendar').fullCalendar('clientEvents');
  
      $.each( allEvents, function( index, value ){
  
          //add event if not exist
          if(value.user_id != userid){
              $('.calendar').fullCalendar( 'renderEvent', myEvent );
          }
      });
  
  }
  </code></pre>
  
  <p>It seams that the event are added even tho the value is added. Is there a better/easyer way to do this?</p>