title: Adding headers after RESTAdapter initialization
body: <p>I am trying to add an <code>Authorization</code> header to my adapter's request after the adapter has been initialized and used.  I can add headers in a static way at the time I create my <code>ApplicationAdapter</code>, but I can't seem to get it use the headers in subsequent REST calls.  I am trying this:</p>
  
  <pre><code>var auth= "Basic " + hash;
  App.ApplicationAdapter.reopen({
      headers: {
          Authorization: auth
      }
  });
  </code></pre>
  
  <p>I have debugged <code>RESTAdapter</code> in the <code>ajax</code> method, and the test for <code>adapter.headers</code> is always <code>undefined</code>.</p>