New method allowing to displace a track along a new direction, up to max the next boundary.

To call this method: #include "Geant/NavigationInterface.h" ... double newdir[3]; // new direction (normalized) double proposed_displacement; ... double actual_displacement = NavigationInterface::DisplaceTrack(track, newdir, proposed_displacement);

In case proposed_displacement hits a boundary, actual_displacement will match the distance to the boundary. The fNexpath field is updated in this case. Other updated fields: fStep (total step), track direction and position. The number of interaction lengths and track time are not updated, this has to be done after by the propagation stage.