message: Add Uncommitted^Sapling.
diff: use pairing::{
  + Field,
  PrimeField,
  PrimeFieldRepr
  };
  @@ -165,6 +166,15 @@ pub struct Note<E: JubjubEngine> {
  }
  impl<E: JubjubEngine> Note<E> {
  + pub fn uncommitted() -> E::Fr {
  + // The smallest u-coordinate that is not on the curve
  + // is one.
  + // TODO: This should be relocated to JubjubEngine as
  + // it's specific to the curve we're using, not all
  + // twisted edwards curves.
  + E::Fr::one()
  + }
  +
  /// Computes the note commitment, returning the full point.
  fn cm_full_point(&self, params: &E::Params) -> edwards::Point<E, PrimeOrder>
  {
  