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

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

  - 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.

  one is working, the other one fails to compute the nearest points although
  it properly computes the distance.

  - test fails on current version.

  adding a test.