title: CTMLoader does not correctly assign the instanceof the geometry
body: <p>if I modify the sample webgl_loader_ctm.html and in the routine callbackModel() add these lines of code:</p>
  
  <pre><code>     if (geometry instanceof THREE.Object3D) alert("THREE.Object3D");
  else if (geometry instanceof THREE.Geometry) alert("THREE.Geometry");
  else alert("Unknown instanceof geometry");
  </code></pre>
  
  <p>I was expecting the second alert to be activated but instead I got the third. As my code depends on the instanceof to be correct, does anybody know what do I have to change in the loader in order to fix this?</p>