400142 ConcurrentModificationException in JDBC SessionManger

As part of this fix, refactored the JDBCSession to remove the SessionData object.
Merge remote-tracking branch 'origin/jetty-7' into jetty-8
Merge remote-tracking branch 'origin/jetty-8'

Conflicts:
	jetty-server/src/main/java/org/eclipse/jetty/server/session/JDBCSessionManager.java