This change makes it so that EntityHuman#setPassengerOf(Entity) invokes
its parent method when leaving vehicles so that VehicleExitEvent is fired
for players leaving vehicles.
This change also fixes BUKKIT-2110, making it so VehicleExitEvent
correctly handles cancellation. The implementation of VehicleExitEvent
completely ignored the cancellation state of the event, making it so that
cancelling the event had no effect. Cancelling a VehicleExitEvent now
causes the entity to remain inside of the vehicle, with no visual stutter.
API has been added to interface with Horses and to modify their inventories. Horse entities will now be recognized with the type EntityType.HORSE, and will no longer be UNKNOWN.
HorseJumpEvent, EntityDamageEvent, and EntityTameEvent are all correctly fired for horses.
This commit fixes BUKKIT-4393.
