resolve: add distinct bus error code for hosts that exist but lack A or AAAA records
dns-domain: fix generation of reverse IP address lookup name
dns-domain: never allow labels that are larger than 63 chars
nss: various minor fixes to nss-myhostname + nss-mymachines
resolved: add small NSS module that uses resolved to resolve DNS names
update TODO
resolved: add legacy dbus service and policy files