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

Factor out some common code from the libm tests. This is a bit messy
because different tests have different ideas about what it means to be
"close enough" to the right answer, depending on the properties of the
function being tested. In the process, I fixed some warnings and
added a few more 'volatile' hacks, which are sufficient to make all
the tests pass at -O2 with clang.

Add tests for conj{,f,l}() that I wrote some time ago. These test the
versions in libm, not the gcc builtins.