Support for setting SessionTrackingMode

Support for setting SessionTrackingMode
Most of this commit is to support invalidating the SSL session by the session manager.
I'm not sure yet that support for SSL session tracking is a good idea. There are quite a few limitations (see the ssl howto doc) and the changes to do it are fairly invasive. The option remains to remove this at a later date and not support SSL session tracking in Tomcat 7.

git-svn-id: https://svn.apache.org/repos/asf/tomcat/trunk@733748 13f79535-47bb-0310-9956-ffa450edef68