Copy stable/9 to releng/9.3 as part of the 9.3-RELEASE cycle.

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

Copy head to stable/9 as part of 9.0-RELEASE release cycle.

Approved by: re (implicit)

signbit() returns nonzero for negative arguments, but we shouldn't assume
that it always returns the same nonzero value.

Don't run tests that assume <= 64-bit precision on machines with quad
precision.

Some basic regression tests for {sin,cos,tan}{,f,l}().