- 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)

Changed the point of collision returned by boxBoxIntersect. The deepest one is returned, instead of the average.

  - do not assume that input vector dir is normalized.

  The conversion formula used is valid only for unit quaternions.
  If a user passes a zero quaternion by mistake, the resulting matrix is
  identity. This is very confusing since multiplying by a Transform3f containing
  0 as a quaternion results in identity Transform3f.

  adding a test.