Fix "setSitting" on tameable animals. Fixes BUKKIT-1534

This makes it so animals (tame or not) will sit properly and not move
around.

Wild animals that are sitting may override the sitting position if
they are attacking.

src/main/java/net/minecraft/server/PathfinderGoalSit.java

@@ -12,7 +12,7 @@ public class PathfinderGoalSit extends PathfinderGoal {
 
     public boolean a() {
         if (!this.a.isTamed()) {
-            return false;
+            return this.b && this.a.aG() == null; // CraftBukkit - Allow sitting for wild animals
         } else if (this.a.H()) {
             return false;
         } else if (!this.a.onGround) {