title: Why do my MongooseJS ObjectIds fail the equality test?
body: <p>Suppose I save and retrieve identical objects as follows</p>
  
  <pre><code>var obj1, obj2;
  
  instance.save(function(err, saved) {
      obj1 = saved;
  });
  
  Model.find(obj1._id).run(function(err, retrieved) {
      obj2 = retrieved;
  });
  </code></pre>
  
  <p>When I print to the console, ObjectIds are the same.  If I call toString on both ObjectIds they are equal.  However doing a straight</p>
  
  <pre><code>obj1._id == obj2._id
  </code></pre>
  
  <p>Returns false.  What is happening here?</p>