I originally didn't plan to include anything like this, but a few people
in #grapevine:computer.surgery pointed out use-cases where it might be
desirable:
- a server that doesn't have enough room to store two full copies of
the db. Transferring a copy over the network to back up is viable.
- making a reflinked copy on a CoW filesystem (we could support this in
the tool, but don't currently)
- a server with some other backup mechanism available like snapshotting
the entire filesystem
