title: ng-pattern doesn't show $error.pattern
body: <p>I have script <a href="http://plnkr.co/edit/PeUIyf42F7eRq83JgWWx?p=preview" rel="noreferrer">here</a> and ng-pattern works correctly because scope.subnet is shown in Output only after input matches pattern. But ng-show doesn't display any error if ng-pattern is not matched</p>
  
  <pre><code>&lt;body ng-contoller="myConfigGenCtr"&gt;
    &lt;form novalidate name="myForm"&gt;
              &lt;div class="form-group"&gt;
                  &lt;label for="hostname"&gt;Firewall hostname&lt;/label&gt;
                  &lt;input type="text" ng-model="hostname" class="form-control" id="hostname"&gt;
              &lt;/div&gt;
              &lt;div class="form-group"&gt;
                  &lt;label for="subnet"&gt;Firewall subnet&lt;/label&gt;
                  &lt;input type="text" ng-model="subnet" class="form-control" id="subnet"
                         required ng-pattern="/^(?:[0-9]{1,3}\.){3}/" &gt;
                  &lt;div class="custom-error"  ng-show="myForm.subnet.$error.pattern"&gt;
                      Not a valid subnet, should be i.e. 10.x.y. (3 bytes only)&lt;/div&gt;
              &lt;/div&gt;
          &lt;/form&gt;
    &lt;div&gt;Output: {{subnet}}&lt;/div&gt;      
  &lt;/body&gt;
  </code></pre>