Upgrade renames/deletions in manifests/ports
The upgrade system needs to handle files that have been deleted in the new release, or have been renamed. Likewise in ports, or even ports that have been deleted or renamed. Handle also files moving to another manifest, or from the base system to a port (or the other direction). Files that are unclaimed should probably be added to an unknown manifest and later be garbage collected when all ports have been upgraded. Marking as release-blocking because we need to keep this under control before old upgraded installations carry around too much old junk.