Random cars will be generated with bloodsplatters on the front.

Self-explanatory. A cosmetic effect to add to the atmosphere, because who says you're the only person who thinks running zombies down in a car is a good way of getting past them?

1/10 cars will start with lots of blood on the external front parts (everything with a mount_dx greater than 0). Only affects pre-placed cars, not the ones spawned in the debug menu.

EDIT: This PR also causes blood only to wash off cars while they are outside in the rain.