We need a separate .rev_db file for each repository we're
tracking. This allows us to track the same logical path off
multiple mirrors. We preserve a symlink to the old .rev_db
(no-UUID) if we're (auto-)migrating from an old version to
preserve backwards compatibility.
Also, get rid of the uuid() wrapper since we cache UUID in our
private config, and the SVN::Ra::get_uuid() function memoizes
the return value per-connection.