Fix EntityDismountEvent changes

While upstream has now made this event cancellable, their changes
result in the vechicle being removed before the event is called,
thus leading cancellation to not behave as expected.

Spigot-Server-Patches/0315-Vehicle-Event-Cancellation-Changes.patch

@@ -0,0 +1,39 @@
+From c39c439f6c3d365e43d812d3cfe4ce7d42b35b2b Mon Sep 17 00:00:00 2001
+From: Zach Brown <zach.brown@destroystokyo.com>
+Date: Fri, 22 Apr 2016 18:20:05 -0500
+Subject: [PATCH] Vehicle Event Cancellation Changes
+
+
+diff --git a/src/main/java/net/minecraft/server/Entity.java b/src/main/java/net/minecraft/server/Entity.java
+index 85358902ff..98d67d9a17 100644
+--- a/src/main/java/net/minecraft/server/Entity.java
++++ b/src/main/java/net/minecraft/server/Entity.java
+@@ -96,7 +96,7 @@ public abstract class Entity implements INamableTileEntity, ICommandListener, Ke
+     public boolean j; public boolean blocksEntitySpawning() { return j; } // Paper - OBFHELPER
+     public final List<Entity> passengers;
+     protected int k;
+-    private Entity ax;
++    private Entity ax;public void setVehicle(Entity entity) { this.ax = entity; } // Paper - OBFHELPER
+     public boolean attachedToPlayer;
+     public World world;
+     public double lastX;
+@@ -2141,6 +2141,7 @@ public abstract class Entity implements INamableTileEntity, ICommandListener, Ke
+             throw new IllegalStateException("Use x.stopRiding(y), not y.removePassenger(x)");
+         } else {
+             // CraftBukkit start
++            entity.setVehicle(this); // Paper - Set the vehicle back for the event
+             CraftEntity craft = (CraftEntity) entity.getBukkitEntity().getVehicle();
+             Entity orig = craft == null ? null : craft.getHandle();
+             if (getBukkitEntity() instanceof Vehicle && entity.getBukkitEntity() instanceof LivingEntity) {
+@@ -2163,6 +2164,8 @@ public abstract class Entity implements INamableTileEntity, ICommandListener, Ke
+                 return;
+             }
+             // Spigot end
++
++            entity.setVehicle(null); // Paper - fix EntityDismountEvent cancellable
+             this.passengers.remove(entity);
+             entity.k = 60;
+         }
+-- 
+2.18.0
+