title: How does toJSON in $firebaseObject work?
body: <p>I forked a normalization example from <a href="http://jsfiddle.net/katowulf/vspo65qm/" rel="nofollow">Kato's fiddle</a> and updated it to the current version of AngularFire and Firebase, you can <a href="http://jsfiddle.net/Fortuna/c5s4mrhw/3/" rel="nofollow">see it here</a>. I tested around a bit to get a better understanding of how <code>$firebaseObject</code> and <code>$firebaseArray</code> work and I really get a hang of it.</p>
  
  <p>Except the <code>toJSON</code> from <code>$firebaseObject</code>.</p>
  
  <p>So I have this little code in the controller:</p>
  
  <pre><code>$scope.singlePost = singleMergedPost('post2');
  console.log('singlePost', $scope.singlePost);
  </code></pre>
  
  <p>The output normally is:</p>
  
  <pre><code>{
    "postData": {
      "bla": "blubb",
      "dateCreated": 1397584465,
      "title": "Another cool website",
      "upvotes": 1,
      "url": "http://www.google.com",
      "user": "simplelogin:2"
    },
    "userData": {
      "email": "kato@firebase.com",
      "jobTitle": "Awesome Dude",
      "name": "Kato Richardson"
    }
  }
  </code></pre>
  
  <p>But when I add <code>toJSON</code> to <code>$extend</code> the output is:</p>
  
  <pre><code>{
    "bla": "blubb",
    "dateCreated": 1397584465,
    "title": "Another cool website",
    "upvotes": 1,
    "url": "http://www.google.com",
    "user": "simplelogin:2"
  }
  </code></pre>
  
  <p>$scope.singlePost actually contains the same data, but I am wondering about:</p>
  
  <ol>
  <li>Why is toJSON even called here, although I haven't sent back any data to the server (at least it looks like from my point of view) yet.</li>
  <li>Why does <code>&lt;pre ng-bind="singlePost | json"&gt;&lt;/pre&gt;</code> only show the <code>postData</code> data?</li>
  </ol>