title: Angular 'orderBy' not working with complex ng-options
body: <p>Can't get <code>orderBy</code> to work when I have a complex <code>ng-options</code> statement.</p>
  
  <p>This does not sort the <code>&lt;select&gt;</code> options as expected:</p>
  
  <p><code>ng-options="p.proxyType for p in proxyOptions track by p.proxyType | orderBy:'proxyType'"</code></p>
  
  <p><a href="http://plnkr.co/edit/60ZbBP1mg5VvlMwrvOZS?p=preview" rel="nofollow">http://plnkr.co/edit/60ZbBP1mg5VvlMwrvOZS?p=preview</a></p>