Update zcash_primitives crate to use ff crate

zcash_primitives/Cargo.toml

@@ -7,6 +7,7 @@ authors = [
 
 [dependencies]
 byteorder = "1"
+ff = "0.4"
 lazy_static = "1"
 pairing = { path = "../pairing" }
 rand = "0.4"

zcash_primitives/src/lib.rs

@@ -3,6 +3,7 @@ extern crate lazy_static;
 
 extern crate blake2_rfc;
 extern crate byteorder;
+extern crate ff;
 extern crate pairing;
 extern crate rand;
 extern crate sapling_crypto;

zcash_primitives/src/transaction/components.rs

@@ -1,8 +1,6 @@
 use byteorder::{LittleEndian, ReadBytesExt, WriteBytesExt};
-use pairing::{
-    bls12_381::{Bls12, Fr, FrRepr},
-    PrimeField, PrimeFieldRepr,
-};
+use ff::{PrimeField, PrimeFieldRepr};
+use pairing::bls12_381::{Bls12, Fr, FrRepr};
 use sapling_crypto::{
     jubjub::{edwards, Unknown},
     redjubjub::{PublicKey, Signature},

zcash_primitives/src/transaction/sighash.rs

@@ -1,6 +1,6 @@
 use blake2_rfc::blake2b::Blake2b;
 use byteorder::{LittleEndian, WriteBytesExt};
-use pairing::{PrimeField, PrimeFieldRepr};
+use ff::{PrimeField, PrimeFieldRepr};
 
 use super::{
     components::{Amount, Script, TxOut},