Adding a cleanup task to remove invalid entities from the spawned mob storage.

src/main/java/com/gmail/nossr50/runnables/MobStoreCleaner.java

@@ -0,0 +1,42 @@
+package com.gmail.nossr50.runnables;
+
+import java.lang.Runnable;
+
+import org.bukkit.Bukkit;
+import org.bukkit.scheduler.BukkitScheduler;
+
+import com.gmail.nossr50.mcMMO;
+
+public class MobStoreCleaner implements Runnable
+{
+    private int taskID;
+
+    public MobStoreCleaner()
+    {
+        taskID = -1;
+        start();
+    }
+
+    public void start()
+    {
+        if (taskID >= 0)
+            return;
+
+        BukkitScheduler scheduler = Bukkit.getServer().getScheduler();
+        taskID = scheduler.scheduleSyncRepeatingTask(mcMMO.p, this, 12000, 12000);
+    }
+
+    public void stop()
+    {
+        if(taskID < 0)
+            return;
+
+        Bukkit.getServer().getScheduler().cancelTask(taskID);
+        taskID = -1;
+    }
+
+    public void run()
+    {
+        mcMMO.p.placeStore.cleanMobLists();
+    }
+}