title: calling python builtin dict on a mock
body: <p>I'd like to be able to setup a mock that allows me to return something when I apply the builtin <code>dict</code> method.</p>
  
  <p>I've tried using <code>__iter__</code> to no avail.  I can't seem to get anything but an empty dictionary:</p>
  
  <pre><code>import mock
  mocked_object = mock.MagicMock()
  mocked_object.__iter__.return_value = [1, 2, 3]
  dict(mocked_object)
  # {}
  </code></pre>