title: angular ui-select and form validation $touched not working together
body: <p>I have this validation-message-tag</p>
  
  <pre><code>&lt;div class="validation-message-tag" ng-show="ctrl.data &amp;&amp; ctrl.$touched"&gt;
    &lt;p ng-repeat="message in success track by $index" class="validation-success"&gt;{{message}}&lt;/p&gt;
    &lt;p ng-repeat="message in info track by $index" class="validation-info"&gt;{{message}}&lt;/p&gt;
    &lt;p ng-repeat="message in warning track by $index" class="validation-warning"&gt;{{message}}&lt;/p&gt;
    &lt;p ng-repeat="message in error track by $index" class="validation-error"&gt;{{message}}&lt;/p&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>And input field using ui-select</p>
  
  <pre><code>      &lt;lable for="tags"&gt;Tags&lt;/lable&gt;
        &lt;div id="tags"&gt;
          &lt;tag-picker-tag ng-model="entity.meta.tags" editable="true" name="tags" check-valid-user-meta-tags&gt;&lt;/tag-picker-tag&gt;
          &lt;validation-message-tag ctrl="form.tags"&gt;&lt;/validation-message-tag&gt;
        &lt;/div&gt;
  </code></pre>
  
  <p>tag-picker-tag: </p>
  
  <pre><code>&lt;div class="tag-picker-tag"&gt;
    tags
    &lt;ui-select ng-model="$parent.tags" ng-disabled="! editable" multiple tagging tagging-tokens="SPACE|," tagging-label="(custom 'new' label)" title="Select tags" sortable="true" theme="bootstrap" &gt;
      &lt;ui-select-match placeholder="Enter Tags..."&gt;{{$item}}&lt;/ui-select-match&gt;
      &lt;ui-select-choices repeat="tag in suggestedTags | filter:$select.search"&gt;
        {{tag}}
      &lt;/ui-select-choices&gt;
    &lt;/ui-select&gt;
    &lt;p&gt;Selected: {{tags}}&lt;/p&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>The validator does fail successfully for invalid input with a correct validation message. But the validation message is not shown because $touched always false. I have tried the same for other input like text area, and only ui-select does not work. </p>
  
  <p>So is there a way to support ui-select with angular $touched field? or is there other boolean flag I can use from ui-select? </p>