Findbugs fixes: implement Cloneable when defining clone method.

git-svn-id: https://svn.apache.org/repos/asf/commons/proper/collections/trunk@1435981 13f79535-47bb-0310-9956-ffa450edef68

src/main/java/org/apache/commons/collections/map/MultiKeyMap.java

@@ -73,7 +73,7 @@ import org.apache.commons.collections.keyvalue.MultiKey;
  * @version $Id$
  */
 public class MultiKeyMap<K, V> extends AbstractMapDecorator<MultiKey<? extends K>, V>
-        implements IterableMap<MultiKey<? extends K>, V>, Serializable {
+        implements IterableMap<MultiKey<? extends K>, V>, Serializable, Cloneable {
 
     /** Serialisation version */
     private static final long serialVersionUID = -1788199231038721040L;