Copy stable/10@r272459 to releng/10.1 as part of
the 10.1-RELEASE process.

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

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

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

Start the dreaded NOFOO -> NO_FOO conversion.

OK'ed by: core

For variables that are only checked with defined(), don't provide
any fake value.

Add a simple exercise suite for IP-level socket options. The suite
atempts to read and write various IP-level socket options as root and
nobody, making sure the initial values are as expected, that they can
be changed to valid values and take effect, etc. No attempt is made
to check for the correct implementation of side effects (such as
changes in packet headers) as yet.

The IP options section is currently broken but will be fixed shortly.

Not all multicast options are currently tested.