add method javadoc as well as class (mainly so it shows up in IDEs, etc. if they have the source present)

Author: David R. MacIver

src/com/rabbitmq/utility/SensibleClone.java

@@ -37,5 +37,10 @@
  * and want to provide some guarantees of the type of the cloned object. 
  */
 public interface SensibleClone<T extends SensibleClone<T>> extends Cloneable {
+
+  /**
+   * Like Object.clone but sensible; in particular, public and declared to return
+   * the right type. 
+   */
   public T sensibleClone();
 }