Bug#460910: libc6: consider defining dns-host.c:MULTI_PTRS_ARE_ALIASES

[Justin Pryzby <jpryzby+d@quoininc.com>]

Package: libc6
Version: 2.6-4
Severity: wishlist

The apparently-unused gethnamaddr.c defines MULTI_PTRS_ARE_ALIASES,
causing "inverse" in-addr.arpa lookups of hosts with multiple PTR
records to contain the first returned hostname in hostent->h_name and
the other hostnames as h_aliases.

However dns-host.c doesn't define this (nor the also-necessary
MAXALIASES), so h_aliases is empty in this context.  It's useful to
have this available, especially since recent bind9 by default does
round-robin ordering for PTRs.

bind9 unconditionally returns multiple ptrs as aliases in
./lib/bind/irs/dns_ho.c.  bind8 seems to do the same.