nss-myhostname: resolve 'localhost' so that /etc/hosts becomes optional
This makes sure nss-myhostname not only resolves the local host name to 127.0.0.2/::1 but also the host name 'localhost: to 127.0.0.1/::1. This makes installation of /etc/passwd optional, as it usually only includes a mapping for 'localhost'. This change also resolves ::1 to the local hostname (as before), but also lists 'localhost' as an alias. This means look-ups are now fully reversible, even though they are 1:n mappings. Finally, the module will no longer erroneously claim that local IP addresses which aren't on the loopback device were.