The rules stay in TrackUneven.h with no dependence on the engine, as they can
be tested. Their use on the tracks moves out of Track.cpp to TrackUneven.cpp,
split into steps: the group of switches, the values of its paths, the meeting
of two ends. One set of helpers for the paths of a track takes the place of
the same conditions written out in several places, and the value at the ends
of a switch is worked out in one place. The clatter of an axle leaves the long
Update of a vehicle. The fields in the editor say themselves when they show.
No change in behaviour.
