This is useful if there are duplicates. Assuming the remote delivers
the entries in a consistent order, this will give the best user
experience in syncing as it will consistently use the first entry for
the sync comparison.
This simplifies the implementation of remotes. The only required
interface is now `List` which is a simple one level directory list.
Optionally remotes may implement `ListR` if they have an efficient way
of doing a recursive list.
