Adding all Entities into CraftBukkit.

These are needed to properly allow for determining class type, in
accordance with current practice.

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

@@ -0,0 +1,18 @@
+package net.minecraft.server;
+
+public class EntityZombieSimple extends EntityMobs {
+
+    public EntityZombieSimple(World world) {
+        super(world);
+        aP = "/mob/zombie.png";
+        bC = 0.5F;
+        c = 50;
+        aZ *= 10;
+        H *= 6F;
+        a(I * 6F, J * 6F);
+    }
+
+    protected float a(int i, int j, int k) {
+        return l.l(i, j, k) - 0.5F;
+    }
+}