title: validation error message not showing for min length when custom validation directive added
body: <p>I want to show error message when the length is lesser than 5, I have tried something like this but its never showing error message "Length must be greated than 5". It works when I remove the attribute equals-to from input tag. How to fix the directive so that its ok with minlength and other validation attributes</p>
  
  <pre><code>&lt;form id="createUserForm" class="form-horizontal row row-full" role="form" name="userForm" novalidate&gt;    
  ...
  &lt;input id="newPassword" name="newPassword" ng-model="newPassword" type="password" ng-minlength="5" equals-to="confirmPassword"&gt;
      &lt;label ng-show="userForm.newPassword.minlength" class="error"&gt;Length must be greater than 4&lt;/label&gt;
  ...
  &lt;/form&gt;
  </code></pre>
  
  <p>javascript</p>
  
  <pre><code>.directive('equalsTo', function() {
      return {
          require: 'ngModel',
          link: function(scope, elm, attrs, ctrl) {
              ctrl.$parsers.unshift(function(viewValue) {
                  if (viewValue === scope[attrs.equalsTo]) {
                      ctrl.$setValidity('equalsTo', true);
                      return viewValue;
                  } else {
                      ctrl.$setValidity('equalsTo', false);
                      return undefined;
                  }
              });
          }
      };
  });
  </code></pre>