Function certifies_flattening2 

pub fn certifies_flattening2(curve: &Curve2) -> bool

Whether crate::curve::flatten2 certifies its chords for this family: every point of the curve then lies within the chord tolerance of the returned polyline (#232). Lines, polylines, circles, ellipses, sinusoids, B-splines with positive weights and arc-length chains whose pieces are all bounded (crate::chain::chain_certifies); other families are flattened on their midpoint sagitta alone, which is a measurement, not a bound.