Correct the documentation for Cluster manager.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/trunk@1545579 13f79535-47bb-0310-9956-ffa450edef68
Expose stateTimestampDrop of org.apache.catalina.ha.session.DeltaManager via JMX.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/trunk@1545582 13f79535-47bb-0310-9956-ffa450edef68