title: Three.js: Bottom of mesh can't be displayed
body: <p>I have converted a mesh from .obj to json using the official converter (<a href="https://github.com/mrdoob/three.js/tree/master/utils/converters/obj" rel="nofollow">https://github.com/mrdoob/three.js/tree/master/utils/converters/obj</a>). The mesh is displayed correctly from one side, but not from the other. I believe the issue is that it only has one side, basically a plane, and therefore all faces and their normals pointing in one direction.</p>
  
  <p>How could I fix this?</p>
  
  <p><strong>Edit:</strong> I could add the mesh twice, and one time using <code>material.side = THREE.BackSide;</code>, but loading it twice doesn't seem like the best option to me.</p>