This is a convenient base class for all classes
that wish to establish an initial identity which
will be the basis of a one-per vm identity: i.e.
in any vm there should only ever be a single object
with a given identity token (except transiently during
canonicalization)
It would be convenient to put the getter/setter methods
for the identity token here, but unfortunately we have no
way of setting up the for Referenceability in multiple
levels of a class hierarchy.