Debian packages conventionally target 'unstable' in their
debian/changelog distribution field, but the series data (the
distro-info CSVs) only knows codenames: the suite is the alias
'unstable' of the series 'sid', a mapping the debian-distro-info tool
resolves internally without exposing it in its data.
Add a per-dist suite_aliases reference-data key (debian: unstable ->
sid), with two helpers on top: resolve_suite_alias, identifying a
changelog suite name with its series codename and the dist that
codename belongs to, and series_suite_alias, the inverse direction.
The two names identify the same series.
vhaudiquet