It should be possible for clones to learn about how to contact
each other without remotes needing to always be explicitly set
up. Say that `.git-annex/remote.log` is maintained by git-annex
to contain:

	UUID hostname URI

The URI comes from configured remotes and maybe from 
`file://$(pwd)`, or even `ssh://$(hostname -f)`
for the current repo. This format will merge without
conflicts or data loss.

Then when content is belived to be in a UUID, and no
configured remote has it, the remote.log can be consulted and
URIs that look likely tried. (file:// ones if the hostname
is the same (or maybe always -- a removable drive might tend
to be mounted at the same location on different hosts),
otherwise ssh:// ones.)

Question: When should git-annex update the remote.log? 
(If not just on init.) Whenever it reads in a repo's remotes?

> This sounds useful and the log should be updated every time any remote is being accessed. A counter or timestamp (yes, distributed times may be wrong/different) could be used to auto-prune old entries via a global and per-remote config setting. -- RichiH