Fix Craft Entity constructors and toStrings.

Also, standardise getHandle and clean up in general.
getHandle is now using the 'entity' member variable instead of
super.getHandle, as this reduces the number of chained calls needed.

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

@@ -1,14 +1,19 @@
 package org.bukkit.craftbukkit.entity;
 
-import net.minecraft.server.Entity;
+import net.minecraft.server.EntityPotion;
 import org.bukkit.craftbukkit.CraftServer;
 import org.bukkit.entity.ThrownPotion;
 
 public class CraftThrownPotion extends CraftProjectile implements ThrownPotion {
-    public CraftThrownPotion(CraftServer server, Entity entity) {
+    public CraftThrownPotion(CraftServer server, EntityPotion entity) {
         super(server, entity);
     }
 
+    @Override
+    public EntityPotion getHandle() {
+        return (EntityPotion) entity;
+    }
+
     @Override
     public String toString() {
         return "CraftThrownPotion";