title: more than one 2d index, not sure which to run geoNear on
body: <p>Why aggregate</p>
  
  <pre><code>    aggregate.near({
        near: coord,
        distanceField: "distance",
        maxDistance: max
      });
  </code></pre>
  
  <p>can return </p>
  
  <pre><code>{
      "name": "MongoError",
      "errmsg": "exception: geoNear command failed: { ok: 0.0, errmsg: \"more than one 2d index, not sure which to run geoNear on\" }",
      "code": 16604,
      "ok": 0
  }
  </code></pre>
  
  <p>having in the scheme the only 2d index:</p>
  
  <pre><code>location: { type: [ Number ], index: '2d', sparse: true },
  </code></pre>
  
  <p>more or less when i remove EVERYTHING from the scheme the error doenst change
  why? o why...</p>