Backup/restore API should have better option to skip 'zip' operatiorn

It is already possible to skip the ‘zip’ operation by specifying the ‘import mode’ but there should be a proper flag for this that only controls the zip operation and does not have any other effects.

• Skipping the zip operation also saves a lot of time.
• The import mode has this effect and doesn’t appear to cause problems, but it seems inappropriate for this use.
• If the import flag actually doesn’t do anything else, then this could just be an alias for the same thing.