- this feature is implemented in a more general way in HPP.

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

  Distance computation between boxes does not seem to be very accurate.

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

  Avoid conflict between fcl official version as installed by ROS and hpp
  modified version.

  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.

  - use API distance function instead of selecting gjk solver.

abs() only works for integers,
replace with std::abs() for floaing point