Adjust to further changes in {utils}/filestorage.
Move interface checks into a test file.
Adjust a doc comment.
Dereference values consistently.
Clarify an error message.
Test against a fake backups storage.
Switch backups archive storage to gridfs.
Move state-specific stuff into the right place.
Close the backups storage when done with it.
Refactor backups metadata storage to use an external session.