Provide native detached entities support

[nealeu]

Whirlwind doesn't currently natively support detached entities, but has historically kept the relationship between an object and it's Ref, in the client session.

Comparing to Hibernate's approach, which is perfectly valid as a comparison, we have neither merge() which merges data from an object into the one in the session, nor update() which expects no object in the session, but adds the detached one in.

For this, we naturally need at least the WW Ref, but will also need version information (which we can keep in the Ref if we wish)

[nealeu]

See http://docs.jboss.org/hibernate/core/3.3/reference/en/html/objectstate.html#objectstate-detached for explanation of merge and update.