message: bigint::monty: simplify modpow parameter init
diff: @@ -106,10 +106,9 @@ pub fn monty_modpow(a: &BigUint, exp: &BigUint, modulus: &BigUint) -> BigUint{
  let mr = MontyReducer::new(modulus);
  // Calculate the Montgomery parameter
  - let mut r : BigUint = One::one();
  - while &r < mr.p {
  - r = r << 32;
  - }
  + let mut v = vec![0; mr.p.data.len()];
  + v.push(1);
  + let r = BigUint::new(v);
  // Map the base to the Montgomery domain
  let mut apri = a * &r % mr.p;
  