Major enhancements to mdnsd nsswitch support:

- nss_mdns renamed to nss_multicast_dns for clarity and less chance of
confusion with nss_mdnsd (see next).
- Support using mdnsd for all unicast too with new nss_mdnsd module
(note: this mode requires an updated mdnsd too, not yet committed)
- Implement resolv.conf "search" directive support. Needed for nss_mdnsd,
potentially useful with nss_multicast_dns (you could now do
"search example.com local" in resolv.conf if you wanted to and it would
act as you might expect)
- Add references in nsswitch.conf man page and sample file
- Implement AI_CANONNAME
- Various bug fixes