title: DropZone.js - Throwing an error on screen immediately after a file is selected
body: <p>I'm using dropzone.js, and trying to figure out how can I throw an error BEFORE the file is shown in the dropzone UI.</p>
  
  <pre><code> Dropzone.autoDiscover = false; 
       var myDropzone = new Dropzone("#fileUpload", { url: "/myUrl/file", maxFiles: 1, maxFilesize: 2,
                      accept: function(file, done) {            
                                      var splitFileName = file.name.split(".");                    
                                      if (splitFileName[splitFileName.length - 1] != "bbb") {                                                                        
                                          done("Error! Files of this type are not accepted");                                    
                                      }
                                      else { done(); }
                                  }                         
                      });
   myDropzone.options.acceptedFiles = '.bbb';
  </code></pre>
  
  <p>Suppose the user drags a file that is not with <code>.bbb</code> extension, then the file is still shown in the dropzone (with an 'X' sign).</p>
  
  <p>Is it possible not to show that file in the dropzone, and even show a relevant error ?</p>