Resin's implementation of the JNDI DirContext.
The actual storage
of the persistent data is in the AbstractModel.
The DirContextImpl is just a Visitor around
the AbstractModel which also encapsulate
the JNDI environment.
In JNDI, each Context is a <model, env> pair.
Each client might pass a different environment
to the InitialContext so each ContextImpl
must be unique for each client.