Poor Cosine accuracy at radians almost equal to 0 or pi/2

[rsinnig]

The maximum relative error of ~0.05 occurs at: 1.570796 < argument < pi/2

A relative error of ~0.01 occurs at: 0 < argument < ~1.7e-6

The mean of relative error is ~1.5E-07 (about 100 times larger than sine). (Test value range -2pi...2pi) The expected difference is a factor of ~10. (Due to even order of approximation polynomial instead of odd order used for sine.)