'tahoe make-tarball' command

[warner]

It would be neat if there were a command to recursively copy a subtree out of a tahoe directory, but instead of writing the files to disk, it would write a tarball to stdout.

This would easily preserve all the usual unix metadata (in particular ownerid/groupid/permissions) which could be stored by a backup tool but which can't normally be set by the recovery tool unless it's working as root. It would also provide a way to handle things that aren't normal files (device nodes, symlinks, etc).

We could also implement the reverse direction: accept a tarball and store its contents in Tahoe.