nss-myhostname: resolve 'localhost' so that /etc/hosts becomes optional

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.