These optimizations gain about 10% performance in the physics code when compiled with /Ox in VC++ 2010
Deriving koord3d from koord simplifies frequently called method koord3d::get_2d()
Fixed: convoys get stuck going downhill.
- downhill frictionfactor is negative.
Merge branch '112.x-private-cars-merge' of git://github.com/BerndGabriel/simutrans-experimental.git into 112.x-private-car-merge
CODE: Attempt to remove dialogue box when depot teleporting is invoked, but not successfully