add javadoc comment to SensibleClone

Author: David R. MacIver

src/com/rabbitmq/utility/SensibleClone.java

@@ -30,6 +30,12 @@
 //
 package com.rabbitmq.utility;
 
+/** 
+ * This interface exists as a workaround for the annoyingness of java.lang.Cloneable.
+ * It is used for generic methods which need to accept something they can actually clone
+ * (Object.clone is protected and java.lang.Cloneable does not define a public clone method)
+ * and want to provide some guarantees of the type of the cloned object. 
+ */
 public interface SensibleClone<T extends SensibleClone<T>> extends Cloneable {
   public T sensibleClone();
 }