s4:libcli/resolve: add getaddrinfo()/dns_looup() resolving

s4:libcli/resolve: add getaddrinfo()/dns_looup() resolving

This "dns_ex" module provides flexible lookup methods
for dns lookups.

The getaddrinfo() part looks at /etc/hosts and dns.
As it handles CNAME replies badly we fallback
to use dns_lookup(name, "A").

The dns_lookup() makes DNS SRV lookups possible.

This module is not a real resolve module, it's just
a generic helper as the nbtlist.c code is.

The next step will be that the "host" module will
use the dns_ex.c code.

metze