Update to modifiation in hpp-corbaserver

  method loadObstacleFromUrdf now takes a prefix.
Add a parameter in Robot python class to avoid reloading the urdf file.
Update to re-organization of collision-checking.
Update to modifications in hpp-model-urdf

  - Freeflyer and planar joints are now composed of 2 and 3-dimensional
    translation joints.
Update to modification in hpp-model

  JointRotation has been split into two classes.