Make uncloneable IO deprecated instead of error, improve error handling (#771)

It appears #754 breaks more code than I thought, so this makes it a soft error (with a runtime deprecation warning - to get people to fix their stuff before we break it for real) for now.

This additionally changes the autoclonetype errors to be more deterministic (reporting class names instead of object names) in the most common cases, to allow the deprecations manager to deduplicate warnings.