Vamos numerical integrator upgrade

[joevenzon]

I upgraded the Vamos numerical integrator from a crappy euler integrator to a fancy velocity-verlet integrator in R1938. Theoretically the integrator is much more stable, conserves energy, and is orders of magnitude more accurate. I can't really tell that there's any difference, but since there's no performance penalty, I'm just going to leave it in there. Let me know if anyone notices weird car physics behavior.