title: $geoIntersects don't work like expected
body: <p>I have a question to the $geoIntersects-Operator. 
  I have the following searchBox and collection-content:</p>
  
  <pre><code>&gt; BOX
  {
          "type" : "Polygon",
          "coordinates" : [
                  [
                          [
                                  0,
                                  0
                          ],
                          [
                                  3,
                                  0
                          ],
                          [
                                  3,
                                  3
                          ],
                          [
                                  0,
                                  3
                          ],
                          [
                                  0,
                                  0
                          ]
                  ]
          ]
  }
  &gt; db.polygon.find()
  { "_id" : "Poly1", "shape" : { "type" : "Polygon", "coordinates" : [  [  [  0, 0 ],  [  3,  0 ],  [  3,  3 ],  [  0, 3 ],  [  0,  0 ] ] ] } } 
  { "_id" : "Poly2", "shape" : { "type" : "Polygon", "coordinates" : [  [  [  3, 0 ],  [  6,  0 ],  [  6,  3 ],  [  3,  3 ],  [  3,  0 ] ] ] } }
  &gt; db.polygon.find( {shape: {$geoIntersects: {$geometry: BOX}}}, {_id:1})
  { "_id" : "Poly1" }
  </code></pre>
  
  <p>Like you can see, the BOX and Poly1 are identical.
  Poly2 shared an edge with BOX.
  So when I was executing the $geoIntersects-Query I was expecting that both polygon’s where returned because of the shared edge, but only Poly1 was found.
  Can somebody explain that to me? Or did I made a stupid mistake I don’t see :(</p>
  
  <p>Auf Wiedersehen, Andre</p>