To behave properly installer properly handles codename/suite
combination. Specially for sid/unstable this is really required
otherwise we can end up trying to configure a broken sources.list.
When figuring out which suite to use, cdrom-detect looks for the
Release file and the first one to be tried is the content of
/etc/default-release, inside of installer initrd, that needs to be
available as symbolic link.
Daniel Baumann
Otavio Salvador