title: Dropzone debug and ajax messages from PHP
body: <p>I'm using latest Dropzone.js release 3.7.1 and PHP script to upload file to server</p>
  
  <p>I'm would like to get message back to drop zone area, on image
  so i exit with</p>
  
  <pre><code>header('HTTP/1.1 500 Internal Server Error');
  header('Content-Type: application/json');
  exit();
  </code></pre>
  
  <p>this display a generic dropzone error on image
  but if i use</p>
  
  <pre><code>header('HTTP/1.1 500 Internal Server Error');
  header('Content-Type: application/json');
  exit("My error");
  </code></pre>
  
  <p>I get "Invalid JSON response from server."</p>
  
  <p>if i use </p>
  
  <pre><code>header('HTTP/1.1 500 Internal Server Error');
  header('Content-type: application/json');
  exit(json_encode(array('message' =&gt; '$msg', code =&gt; 500)));
  </code></pre>
  
  <p>i get "[object Object]"</p>
  
  <p>Does drop zone pass file upload as an array or as a single file?</p>