Allow teleportation of entities on vehicles. Fixes BUKKIT-4210

Up until Minecraft version 1.5 it was not possible to teleport entities
within vehicles. With the 1.5 update came the change in the Minecraft
teleportation logic to dismount before teleporting the entity, if
applicable.

This commit ammends the existing CraftBukkit logic for rejecting
teleportation for entities in vehicles to permit the action. Due to this
change, CraftBukkit is now in-line with Minecraft 1.5 teleportation logic.

src/main/java/org/bukkit/craftbukkit/entity/CraftEntity.java

@@ -201,10 +201,13 @@ public abstract class CraftEntity implements org.bukkit.entity.Entity {
     }
 
     public boolean teleport(Location location, TeleportCause cause) {
-        if (entity.vehicle != null || entity.passenger != null || entity.dead) {
+        if (entity.passenger != null || entity.dead) {
             return false;
         }
 
+        // If this entity is riding another entity, we must dismount before teleporting.
+        entity.mount(null);
+
         entity.world = ((CraftWorld) location.getWorld()).getHandle();
         entity.setLocation(location.getX(), location.getY(), location.getZ(), location.getYaw(), location.getPitch());
         // entity.setLocation() throws no event, and so cannot be cancelled

src/main/java/org/bukkit/craftbukkit/entity/CraftPlayer.java

@@ -458,7 +458,7 @@ public class CraftPlayer extends CraftHumanEntity implements Player {
             return false;
         }
 
-        if (entity.vehicle != null || entity.passenger != null) {
+        if (entity.passenger != null) {
             return false;
         }
 
@@ -475,6 +475,9 @@ public class CraftPlayer extends CraftHumanEntity implements Player {
             return false;
         }
 
+        // If this player is riding another entity, we must dismount before teleporting.
+        entity.mount(null);
+
         // Update the From Location
         from = event.getFrom();
         // Grab the new To Location dependent on whether the event was cancelled.