title: Can't resolve RSVP.Promise in QUnit integration test
body: <p>I am writing an integration test for my Ember.js application in QUnit. Before a test, I want to seed some test data by issuing HTTP requests to a dedicated testing API. I use <code>jQuery.post</code> to issue POST requests and I use <code>Ember.RSVP.Promise.cast</code> to turn the jQuery promise into an RSVP promise. However, it never seems to resolve. In the code below, it just hangs. The string <code>"STARTING"</code> is printed but neither <code>"DONE"</code> nor <code>"FAIL"</code> is printed.</p>
  
  <p>I also tried creating a new RSVP Promise as described in the "Advanced usage" section of <a href="http://emberjs.com/api/classes/Ember.RSVP.Promise.html" rel="nofollow">http://emberjs.com/api/classes/Ember.RSVP.Promise.html</a>, to no avail (it also hanged). If I don't wrap the jQuery promise into an  RSVP Promise, it does reach either the <code>"DONE"</code> or <code>"FAIL"</code>.</p>
  
  <p>Why doesn't the RSVP Promise resolve?</p>
  
  <pre><code>function create_teacher() {
    var url = "&lt;%= testing_teacher_path %&gt;";
  
    return Ember.RSVP.Promise.cast(
      Ember.$.post(
        url,
        {
          user: {
            first_name: "John",
            last_name: "Doe"
            school: "EE3",
            email: "john@doe.com",
            password: "password"
          }
        }
      )
    );
  }
  
  module("Teacher Dashboard", {
    setup: function() {
      console.log("STARTING");
      Ember.run(HstryEd, HstryEd.advanceReadiness);
    },
    teardown: function() {
      console.log("TEARING DOWN");
      HstryEd.reset();
    }
  });
  
  asyncTest("Login", function() {
    expect(1);
  
    var teacher = create_teacher();
    teacher.then(function() {
      console.log("DONE");
      ok(true, "done");
      start();
    },
    function() {
      console.log("FAIL");
      ok(false, "fail");
      start();
    });
  });
  </code></pre>