title: input type file is Firing Twice onchange()
body: <p>I have this script </p>
  
  <p><strong>Update:</strong></p>
  
  <pre><code>/*on document ready*/
  $(function() {
  UploadFile();
  }
  
  function UploadFile(){
      $('#formarea').on('change', '.btn-file :file', function() {
          var input = $(this),
          numFiles = input.get(0).files ? input.get(0).files.length : 1,
          label = input.val().replace(/\\/g, '/').replace(/.*\//, '');
          input.trigger('fileselect', [numFiles, label]);
          alert('test');/*this showing two time*/
      });
      $('#formarea').on('fileselect','.btn-file :file', function(event, numFiles, label) {
          var input = $(this).parents('.input-group').find(':text'),
          log = numFiles &gt; 1 ? numFiles + ' files selected' : label;
          if( input.length ) {
              input.val(log);
          } else {
              if( log ) alert(log);
          }
      });
  }
  </code></pre>
  
  <p>and i have this field on the form:</p>
  
  <pre><code>&lt;form id='formarea'&gt;
  &lt;div class="form-group"&gt;
                                  &lt;label class="col-lg-3 control-label"&gt;Documento Adjunto:&lt;/label&gt;
                                  &lt;div class="col-lg-12 has-warning"&gt;
                                      &lt;div class="input-group"&gt;
                                          &lt;span class="input-group-btn"&gt;
                                              &lt;span class="btn btn-primary btn-file"&gt;
                                                  buscar&amp;hellip; &lt;input id='file' type="file" name='i_file_1'&gt;
                                              &lt;/span&gt;
                                          &lt;/span&gt;
                                          &lt;input type="text" class="form-control" readonly&gt;
                                      &lt;/div&gt;
                                  &lt;/div&gt;
                              &lt;/div&gt;
  &lt;/form&gt;
  </code></pre>
  
  <p>The problem is that onchange is firing twice the <code>alert</code>/ <code>alert('test');</code>  / of javascript is showing two time.
  I need the state on input filled with a file to start a filter file extention.</p>