title: Dropzone JS throws "undefined" when adding "error event"
body: <p>My Dropzone is limited to 2 Files ( maxFiles: 2). If the user drags a new File into the Dropzone, the maxfileexceeds event shows an error.</p>
  
  <pre><code>myDropzone.on("maxfilesexceeded", function(file){
          alert("no more files accepted");
          myDropzone.removeFile(file);
      })
  </code></pre>
  
  <p>But:
  If I add the "error event"..</p>
  
  <pre><code>myDropzone.on("error", function(file, errormessage, response){
          alert(response.message);
      })
  </code></pre>
  
  <p>to get a response if something fails, Dropzone alerts an "undefined".
  The params on the error event should be correct..
  Qoute(DropzoneJS homepage):</p>
  
  <blockquote>
    <p>error: An error occured. Receives the errorMessage as second parameter and if the error was due to the XMLHttpRequest the xhr object as third. </p>
  </blockquote>
  
  <p>So the first param is the file, second an errormessage (according to the author) and the 3rd param is a error which comes from the server.</p>
  
  <p>The error response on the server looks like this:</p>
  
  <pre><code>$response = array('status' =&gt; 'error', 'message' =&gt; 'unknown error occured');
  
  header('HTTP/1.1 500 Internal Server Error');
  header('Content-type: application/json');
  $response["message"] = $message;
  exit (json_encode($response));
  </code></pre>
  
  <p>so why does Dropzone give me an "undefined" ?</p>