title: .trigger('chosen:updated') does not work... Chosen v1.6.1
body: <p>So I have this in my cshtml...</p>
  
  <pre><code> @Html.ListBoxFor(model =&gt; model.RoleHelper.roleIDs, ViewBag.Roles as MultiSelectList, new { @id = "roles", @name="roles", @class = "chosen-select", data_placeholder = "Select Role..." })
  </code></pre>
  
  <p>I have activated chosen by using this:</p>
  
  <pre><code>&lt;script&gt;    $(".chosen-select").chosen({ width: "100%", display_selected_options: false });&lt;/script&gt;
  </code></pre>
  
  <p>Then I have a button:</p>
  
  <pre><code>&lt;input type="button" onclick="selAll()" id="select_all" name="select_all" value="Select All"&gt;
  </code></pre>
  
  <p>Which calls this function:</p>
  
  <pre><code>&lt;script&gt;
  function selAll()
  {
      $('#roles option').prop('selected', true).trigger('chosen:updated');
      alert("test");
  }&lt;/script&gt;
  </code></pre>
  
  <p>Basically what I want to do is when the button is clicked, all the roles in my roles multiselect box is selected. Problem is, my chosen-enabled multi select box does not reflect this change. I can see that all the options are selected, but chosen does not update. (By updated I mean, the options are not shown)</p>
  
  <p>Chosen is also not updated when I tried to dynamically populate the options of one of my multi select boxes. This is after I called .trigger('chosen:updated').</p>
  
  <p>Can anyone please tell me what I did wrong? And how to solve this...</p>
  
  <p>BTW: The alert works meaning that $('#roles option').prop('selected', true).trigger('chosen:updated'); is called successfully...</p>