- The frame in which closest points were expressed was neither clear, nor
    consistent.

  This enables users to install the official version of fcl together with
  hpp-fcl.

  - returning a small value for the distance lower bound makes time of
    computation of continuous collision checking very high. It is better to
    break the bounding volumes to get a better bound, eventhough it increases
    the time of computation.

  - throw exception if called.

  - in class CollisionTraversalNodeBase and derived classes.

  sqrt should be applied after method call.

  enable_distance_lower_bound.

  - add a Boolean value in CollisionRequest to trigger this option,
  - if selected, fcl::collision function will compute a lower bound
    on the distance between the two objects if they do not collide.

  - copied code from Wildmagic (http://www.geometrictools.com) nodified
    boost license.
  - collision detection calls distance function.

- The convention of FCL is object1 --> object2
- mesh-mesh:   object1 --> object2 (correct)
- shape-shape: object2 --> object1 (fixed)
- shape-mesh:  object2 --> object1 (fixed)