title: AngularJS: read only input with ng-readonly
body: <p>I have a weird problem with passing a boolean to a text. Here is <a href="http://jsfiddle.net/anvarik/3cnV9/3/">jsfiddle</a></p>
  
  <pre><code>&lt;div ng-app ng-controller="MainCtrl"&gt;
      &lt;p&gt;First Name:
      &lt;input ng-model="first" ng-readonly="true"/&gt;
      &lt;/p&gt;
      &lt;p&gt;Last Name:
          &lt;input ng-model="second" ng-readonly="{{truefalse}}"/&gt;
      &lt;/p&gt;
  &lt;/div&gt;
  
  function MainCtrl($scope) {
      $scope.first = "Angular";
      $scope.second = "JS";
      $scope.truefalse = "true";
  }
  </code></pre>
  
  <p>Can someone explain me why second field is still modifiable?</p>