Fix https://issues.apache.org/bugzilla/show_bug.cgi?id=56698
When persisting idle sessions, only persist newly idle sessions. Patch provided by Felix Schumacher.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/tc7.0.x/trunk@1608448 13f79535-47bb-0310-9956-ffa450edef68