This changes the default remote.origin.fetch configuration
created by git-clone so that it allows non-fast-forward updates.
When using the separate-remote layout with reflog enabled, it
does not make much sense to refuse to update the remote tracking
branch just because some of them do not fast-forward. git-fetch
issues warnings on non-fast-forwardness, and the user can peek
at what the previous state was using the reflog.