ContainerFactory creates the appropriate Container instance
(StatefulSessionContainer, StatelessSessionContainer, EntityContainer,
MessageBeanContainer) and initializes it.
It is also a factory for EJBObject/Home instances which are needed
by the Protocol Manager when a remote invocation arrives.
Return the container factory's TransactionManager object.
Called from SerialContext during JNDI lookup at
"java:pm/TransactionManager". Note that the container's
TransactionManager is a wrapper over the real TM.