- accept only four-element arrays for bezier(): extra values make the curve
malformed, so it falls back to linear like the other invalid forms (#1884);
- stop Newton on the estimated y error (f * dy/dx) instead of a residual in x
alone: near the endpoints dy/dx is in the thousands, so a 1e-9 residual in x
could still move the returned value;
- tests: a five-element curve is linear, and three steep curves match a
bisection reference within 1e-6.
Camille Moine
efcdad04af