VFPU: Ensure that sin(4*x) returns 0.0 (and cos 1) for all x. Fixes #2921
Fix silly mistake in vfpu_sincos. Add unittest.
Merge pull request #6329 from hrydgard/vfpu-sincos

VFPU: Ensure that sin(4*x) returns 0.0 (and cos 1) for all x. Fixes #2921