add getLastKey()

uk/ac/sanger/artemis/util/CacheHashMap.java

@@ -64,6 +64,11 @@ public class CacheHashMap extends HashMap<Object, Object>
     return super.get(key);
   }
 
+  public Object getLastKey()
+  {
+    return accessList.getLast();
+  }
+  
   private void shrink() 
   {
     final Iterator<Object> it = accessList.iterator();