pub/ed25519.c: Range-check coordinates and scalars when verifying.

pub/ed25519.c: Range-check coordinates and scalars when verifying.

This is a requirement of RFC8032, though Bernstein et al don't see the
point.

It's easy enough to test that verification rejects an out-of-range
scalar part in the signature, but there's hardly any space in the
curve-point part, so I've had to cheat.