When there's just 1 client repo, and a transfer repo is created, its
preferred content will now make it prefer all content in the client,
even though there's no other client yet to transfer it to. Presumably,
another client will be created eventually. It might even already exist,
and the transfer repo will be used to connect up with it.
I've designed these to work well together, I hope. If I get it wrong,
I can just change the code in one place, since these expressions
won't be stored in the git-annex branch.
