in= was problimatic in two ways. First, it referred to a remote by name,
but preferred content expressions can be evaluated elsewhere, where that
remote doesn't exist, or a different remote has the same name. This name
lookup code could error out at runtime. Secondly, in= seemed pretty useless.
in=here did not cause content to be gotten, but it did let present content
be dropped.
present is more useful, although "not present" is unstable and should be
avoided.
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.
