Fixed equals methods for better efficiency.
Cleaned up ClusterService API.
diff --git a/core/api/src/main/java/org/onlab/onos/cluster/ClusterEventListener.java b/core/api/src/main/java/org/onlab/onos/cluster/ClusterEventListener.java
new file mode 100644
index 0000000..5cc4ea0
--- /dev/null
+++ b/core/api/src/main/java/org/onlab/onos/cluster/ClusterEventListener.java
@@ -0,0 +1,9 @@
+package org.onlab.onos.cluster;
+
+import org.onlab.onos.event.EventListener;
+
+/**
+ * Entity capable of receiving device cluster-related events.
+ */
+public interface ClusterEventListener extends EventListener<ClusterEvent> {
+}