session colocation

this is a longstanding WADI innovation (NYI) which has been picked up on and used by the Geronimo session API. As a consequence, we may have actually implement it our end in order to integrate, although i think it is not required for the first cut...

It is an interesting idea which no appserver should be without - basically, related sessions are stored in a 'super' session, so that they are all migrated together to the same location, when evacuated etc...

This is related to : http://jira.codehaus.org/browse/WADI-26, for which I have a solution in mind...

I don't like the G-session-api because it exposes this colocation to the container. I think that colocatio should be a pluggable policy and the client container should not need to be aware of whether WADI is colocating or not - otherwise a container running in a standalone situation is burdened with an API that is irrlelvant to it.... etc...