Copy head (r256279) to stable/10 as part of the 10.0-RELEASE cycle.

Approved by: re (implicit)
Sponsored by: The FreeBSD Foundation

Merge IGMPv3 and Source-Specific Multicast (SSM) to the FreeBSD
IPv4 stack.

Diffs are minimized against p4.
PCS has been used for some protocol verification, more widespread
testing of recorded sources in Group-and-Source queries is needed.
sizeof(struct igmpstat) has changed.

__FreeBSD_version is bumped to 800070.

Options spring cleanup:
- Add and document the KVM and KVM_SUPPORT options that
are needed for the ifmcstats(3) makefile
- Garbage collect unused variables
- Add missing inclusion of bsd.own.mk where needed

Approved by: kan (mentor)
Reviewed by: ru

Considerably rework the ifmcstat utility.
* Build with or without INET, INET6, or KVM features.
* When built without KVM, the sysctl-based getifmaddrs() function
is used as the back-end for the utility.
* Reflect the fact that FreeBSD now uses the in_multi refcount as
a true refcount.
* Style.

The utility may now be run without super-user privilege, albeit with
a less detailed display, equivalent to that of the soon-to-be-retired
netstat -g host-mode output.

MFC after: 3 weeks

Make clean for !INET6.
Remove non-FreeBSD code.
Sort includes.

Remove unused variable and clamp down with WARNS=2

PR: 71662
Submitted by: Dan Lukes <dan@obluda.cz>
Tested on: i386, sparc64, ia64, amd64

style.Makefile(5)

Perform a major cleanup of the usr.sbin Makefiles.
These are not perfectly in agreement with each other style-wise, but they
are orders of orders of magnitude more consistent style-wise than before.

Install it with mode 550, and with default group ${BINGRP}.

drop setgid bit. ifmcstat(8) is not audited, and is needed only for root.

Obtained from: KAME
MFC after: 1 week

- Backout botched attempt to introduce MANSECT feature.
- MAN[1-9] -> MAN.

Set the default manual section for usr.sbin/ to 8.

Getaddrinfo(), getnameinfo(), and etc support in libc/net.
Several udp and raw apps IPv6 support.

Reviewed by: freebsd-arch, cvs-committers
Obtained from: KAME project