More to vehicle internals.

Set-back handling:
* Make the VehicleSetBack a class in the moving package.
* For set-backs use the debug flag from the time of checking.

Debugging:
* Alter debug output for moves slightly (differing locations).
* Add debug output for vehicle moves with players involved.

Note on 1.6:
* Not even PlayerMove is fired for pigs and horses, so no tracking.