Vehicle rotation on map generation is still wrong

[ianestrachan]

mapgen.cpp's map::rotate rotates vehicle directions, but doesn't actually change the vehicles' locations, requiring direction-specific placement for vehicles.

I'd like to say that this is the root cause of vehicle weirdness (clipping into other vehicles or through walls) but it's about the third time I've found something that seems to be causing those issues, so I'll hold back this time.

It certainly can cause things like random holes in walls and absurdly damaged vehicles that are separated from each other, because this happens:

• Map is generated
• Vehicle is placed, intersects wall, wall is destroyed and vehicle is smashed
• Map is rotated, everything except the vehicle moves
• Vehicle is now clipping through another wall, and not anywhere near the original wall it smashed up