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

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

Raise WARNS for various tools where possible.

Submitted by: Marius Nünnerich <marius@nuenneri.ch>

These are WARNS=5 clean, mark them as such to keep them that way.

Look at by: sebastian.ssmoller@web.de on audit@

Default to WARNS=2.
Binary builds that cannot handle this must explicitly set WARNS=0.

Reviewed by: mike

Add kldconfig(8), a utility to modify the kernel module search path.

Reviewed by: -arch, -audit