title: ng-readonly not working in angular checkbox
body: <p>Can I use ng-readonly directive in a checkbox?</p>
  
  <p>The checkbox is writable even after it is decorated with ng-readonly.</p>
  
  <p>Html: </p>
  
  <pre><code>&lt;input type="checkbox" ng-model="model" ng-readonly="test" /&gt; {{model}}
  </code></pre>
  
  <p>Controller:</p>
  
  <pre><code>myApp.controller('MyCtrl', function($scope) {
      $scope.test = true;
  });
  </code></pre>
  
  <p>Added <a href="http://jsfiddle.net/HB7LU/19998/" rel="noreferrer">Fiddle</a></p>