Implemented WorldUnloadEvent and unloadWorld().

src/main/java/org/bukkit/event/world/WorldListener.java

@@ -57,6 +57,13 @@ public class WorldListener implements Listener {
         throw new AuthorNagException("onWorldLoad has been replaced with a new signature, (WorldLoadEvent)");
     }
 
+    /**
+     * Called when a World is unloaded
+     *
+     * @param event Relevant event details
+     */
+    public void onWorldUnload(WorldUnloadEvent event) { }
+
     // TODO: Remove after RB
     @Deprecated public void onWorldLoad(WorldEvent event) {}
     @Deprecated public void onWorldSave(WorldEvent event) {}

src/main/java/org/bukkit/event/world/WorldUnloadEvent.java

@@ -0,0 +1,21 @@
+package org.bukkit.event.world;
+
+import org.bukkit.World;
+import org.bukkit.event.Cancellable;
+
+public class WorldUnloadEvent extends WorldEvent implements Cancellable {
+
+    private boolean isCancelled;
+
+    public WorldUnloadEvent(World world) {
+        super(Type.WORLD_UNLOAD, world);
+    }
+
+    public boolean isCancelled() {
+        return this.isCancelled;
+    }
+
+    public void setCancelled(boolean cancel) {
+        this.isCancelled = cancel;
+    }
+}