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

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

Remove leaf node WARNS?=2 (that mainly I added). This should
help the GCC3 transition and CURRENT in general.

Warns cleanups.

Bring in an old faithful tool I've been using for just over 4 years now
(originally on a different OS without mkstemp()), albeit somewhat
bashed and hacked into something that doesn't look too much like
the original any more. It should be upwardly compatable with
OpenBSD's mktemp(1) but does a couple of extra things.

I've taken OpenBSD's mktemp.1 man page and adapted it to suit.