title: Disable re-select when model was selected in Angularjs-chosen
body: <p>I need help with the following scenario:</p>
  
  <p>I use a single-select dropdowns in a table. Each row has its own dropdown.
  Now there are 2 options for changing the selection:</p>
  
  <ol>
  <li><p>Click on deselect ('x') icon (works ok - via ng-change).</p></li>
  <li><p>Open the dropdown, choose another value from list. Override the previous value (although ng-change fires, I have no way to know if it's a new value or a overriding value).</p></li>
  </ol>
  
  <p>I wish to disable the second behavior. Is it possible to 'tell' chosen that once a value was selected, the only way to re-select a new value is to click on 'x'?
  e.g: once a value was selected, disable the dropdown, hide the 'arrow' icon, but keep the 'x' deselect icon active?</p>
  
  <pre><code>&lt;select chosen
                              allow-single-deselect="true"
                              placeholder-text-single="'Select'
                              ng-model="row.userSelection"
                              ng-options="field as field.name for field in vm.fields"&gt;
                          &lt;option value=""&gt;&lt;/option&gt;
                      &lt;/select&gt;
  </code></pre>
  
  <p>Thanks.</p>