Answer a number >= 0 which represents the current version of the
object's representation. The default implementation answers
zero.
convertFromVersion: version withFixedVariables: fixed indexedVariables: indexed for: anObjectDumper
This method is called if a VersionableObjectProxy is attached to
a class. It receives the version number that was stored for the
object (or nil if the object did not use a VersionableObjectProxy),
the fixed instance variables, the indexed instance variables,
and the ObjectDumper that has read the object.
The default implementation ignores the version and simply fills
in an instance of the receiver with the given fixed and indexed
instance variables (nil if the class instances are of fixed size).
If instance variables were removed from the class, extras are
ignored; if the class is now fixed and used to be indexed,
indexed is not used.
nonVersionedInstSize
Answer the number of instance variables that the class used to have
when objects were stored without using a VersionableObjectProxy.
The default implementation answers the current instSize.