r42Gamma1

[Chris Muller]

I have just posted Magma r42Gamma1 to SqueakMap and SqueakSource.

gamma1 over beta3:

- The RepositoryDefinition now maintains a canonicalized Set of
MagmaForwardingProxy 'links' to objects in other repositories,
including their canonicalized MagmaId's.  This allows easier
deployment / movement of repositories in multi-repository federations.

- Don't antagonize a proxy during preSerialization, nor when obtaining
the objectCountByClass of a Session.

- More strict error-check for sharing objects across sessions.

- Fix not-caching lastKnownSize of an empty MagmaCollectionReader.

- The commits.log file is being written during a fullBackupTo:.  Don't copy it.

- Minor fixes to MagmaFileTraverser.