fix travel speeds for cars

It seems the car profile is scaling speeds by 2/3, even when no maxspeed isset. In other words, motorways which have 90 km/h specified in the speed profile end up with 60 km/h.

This commit fixes this, and activates some speed tests. It also rewrites a few relevant tests so they test for speed directly, rather that test for travel time. This makes it easiser to see what's going on.

Btw, I think that scaling by 0.66 might be a bit too conservative. maybe 0.8 would be more realistic?