Consider replacing synchronized maps with util.concurrent version in session replication

JBossCacheManager could almost certainly benefit by replacing a synchronized HashMap of sessions with Concurrent(Reader)HashMap. Probably not the reader version as many threads can be adding/removing sessions.

Take a look at ClusteredSession's maps as well, although my inclination is not to change these. These fields are inherited from the TC superclass and I'd prefer to stay close to TC. In any case, there should not be a lot of concurrent access to an individual session object.