Fix a problem where zero-length RDATA fields can cause named(8) to crash.

Fix a problem where zero-length RDATA fields can cause named(8) to crash.
[12:03]

Correct a privilege escalation when returning from kernel if
running FreeBSD/amd64 on non-AMD processors. [12:04]

Fix reference count errors in IPv6 code. [EN-12:02]

Security:	CVE-2012-1667
Security:	FreeBSD-SA-12:03.bind
Security:	CVE-2012-0217
Security:	FreeBSD-SA-12:04.sysret
Security:	FreeBSD-EN-12:02.ipv6refcount
Approved by:	so (simon, bz)

git-svn-id: svn://svn.freebsd.org/base/stable/8@236953 ccf9f872-aa2e-dd11-9fc8-001c23d0bc1f