3661 Sync mDNS with upstream
Reviewed by: Richard Lowe <richlowe@richlowe.net>
Approved by: Robert Mustacchi <rm@joyent.com>

6795445 mdnsd holds onto /etc/resolv.conf, leaks file descriptor
6741196 mdnsd parse DNS server list error on console when resolv.conf doesn't exist

PSARC 2005/562 Multicast DNS and Service Discovery
6550311 Multicast DNS and service discovery support