project file: back to single thread.
Merge branch '112.5-merge' of git@github.com:BerndGabriel/simutrans-experimental.git into 112.5-merge
Enhanced: vehikel_basis_t caches grund_t and weg_t of its current position.
- avoids several redundant calls to time consuming lookup() and get_way().
Enhanced: increment_odometer() saves some calls to time consuming add_running_cost().
Changed: moved INT_CHECKS from generate_passengers_or_mail() to step_passengers_or_mail()