title: Requirejs' order does not work with priority config and CDN dependencies
body: <p>The following <code>main.js</code> code do not respect the order of priorities (sometimes <code>underscore.js</code> is not loaded when <code>backbone.js</code> needs it):</p>
  
  <pre><code>require({
      baseUrl:'/scripts',
      priority:[
          "http://ajax.googleapis.com/ajax/libs/jquery/1.5.2/jquery.min.js",
          "http://ajax.googleapis.com/ajax/libs/jqueryui/1.8.12/jquery-ui.min.js",
          "http://ajax.cdnjs.com/ajax/libs/underscore.js/1.1.6/underscore-min.js",
          "http://ajax.cdnjs.com/ajax/libs/backbone.js/0.3.3/backbone-min.js"
      ]
      },["src/app"], 
      function (app) {
          app.start();
  });
  </code></pre>
  
  <p>Adding <code>order!</code> before those CDN dependencies fails with a <code>order.js not found</code> error.</p>