message: Add test that torsion doesn't affect signature verification.
diff: @@ -155,10 +155,39 @@ mod tests {
  use pairing::bls12_381::Bls12;
  use rand::thread_rng;
  - use jubjub::JubjubBls12;
  + use jubjub::{JubjubBls12, fs::Fs, edwards};
  use super::*;
  + #[test]
  + fn cofactor_check() {
  + let rng = &mut thread_rng();
  + let params = &JubjubBls12::new();
  + let inf = edwards::Point::zero();
  + let p_g = FixedGenerators::SpendingKeyGenerator;
  +
  + let p8 = loop {
  + let r = edwards::Point::<Bls12, _>::rand(rng, params).mul(Fs::char(), params);
  +
  + let r2 = r.double(params);
  + let r4 = r2.double(params);
  + let r8 = r4.double(params);
  +
  + if r2 != inf && r4 != inf && r8 == inf {
  + break r;
  + }
  + };
  +
  + let sk = PrivateKey::<Bls12>(rng.gen());
  + let vk = PublicKey::from_private(&sk, p_g, params);
  + let msg = b"Foo bar";
  + let sig = sk.sign(msg, rng, p_g, params);
  + assert!(vk.verify(msg, &sig, p_g, params));
  +
  + let vktorsion = PublicKey(vk.0.add(&p8, params));
  + assert!(vktorsion.verify(msg, &sig, p_g, params));
  + }
  +
  #[test]
  fn round_trip_serialization() {
  let rng = &mut thread_rng();
  