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

Add regression tests for fmin{,f,l} and fmax{,f,l}.
I wrote these to test amd64 asm functions that used
maxss, maxsd, minss, and minsd, but it turns out that
those instructions don't handle NaNs and signed zero
in the same way as fmin() and fmax() are required to,
so we're stuck with the C versions for now.