Some miscellaneous improvements

[tagener-noisu]

• Heli pilot ignores target that are behind him, which is ok for ground targets, but not air targets. Fixed it.
• When the path action says exit the vehicle for passengers only, everyone leaves except the driver. It's a problem for vehicles that have a separate gunner on the second slot, for example AMTRAC. I added a way to set in config who is to leave the vehicle.
• When config says not to use air vehicles, bots shouldn't go to vehicle paths for air vehicles.