if you're trying to tombstone at the head of the desk, you probably
don't know what you're doing. so we abort.
we keep the option to `|rm` any matching hashes in other desks since
this is something the tombstoner might not know exists in advance and is
actively blocking them from completing the desired tombstone operation.
wasn't properly descending into directories next to files with the same
name.
now offers to remove files that can't be tombstoned. can choose to
remove the file at the head of the current desk or from the files on
other desks sharing the same hash.