'RELENG_7_0_0_RELEASE'.

This commit was manufactured to restore the state of the 7.0-RELEASE image.

  http://www.opengroup.org/onlinepubs/009695399/functions/gethostbyaddr.html

gethostbyaddr_r() is changed as well.
It breaks ABI backward compatibility on 64 bit arch.  So, we fix it
on 32 bit arch only for now.

Reported by:	Rostislav Krasny <rosti.bsd@gmail.com>

  expose them to outside of libc.
- make netdb functions NSS friendly.

Reviewed by:	arch@ and current@ (no objection)

Since, res_sendsigned(3) and the friends use MD5 functions, it is
hard to include them without having MD5 functions in libc.  So,
res_sendsigned(3) is not merged into libc.

Since, res_update(3) in BIND9 is not binary compatible with our
res_update(3), res_update(3) is leaved as is, except some
necessary modifications.
The res_update(3) and the friends are not essential part of the
resolver.  They are not defined in resolv.h but defined in
res_update.h separately in BIND9.  Further, they are not called from
our tree.  So, I hide them from our resolv.h, but leave them only
for binary backward compatibility (perhaps, no one calls them).

Since, struct __res_state_ext is not exposed in BIND9, I hide it
from our resolv.h.  And, global variable _res_ext is removed.  It
breaks binary backward compatibility.  But, since it is not used from
outside of our libc, I think it is safe.

Reviewed by:	arch@ (no objection)

IPv6 address when RES_USE_INET6 was set, according to RFC 2133
section 6.2.