Add history information about this renaming in Slave class javadocs

core/src/main/java/hudson/model/Slave.java

@@ -82,6 +82,11 @@ import org.kohsuke.stapler.StaplerResponse;
  * <p>
  * TODO: move out more stuff to {@link DumbSlave}.
  * 
+ * On Febrary, 2016 a general renaming was done internally: the "slave" term was replaced by
+ * "Agent". This change was applied in: UI labels/HTML pages, javadocs and log messages.
+ * Java classes, fields, methods, etc were not renamed to avoid compatibility issues.
+ * See <a href="https://issues.jenkins-ci.org/browse/JENKINS-27268">JENKINS-27268</a>.
+ *
  * @author Kohsuke Kawaguchi
  */
 public abstract class Slave extends Node implements Serializable {