Downgrade to rust-elements v0.16.0

A regression introduced in v0.17.0 made `Value` incompatible with
bincode: ElementsProject/rust-elements#96

This also requires downgrading rust-bitcoin to v0.26, to match the
version used by rust-elements.

This reverts commit 2759c50.

Author: shesek

Cargo.lock

@@ -22,11 +22,11 @@ arraydeque = "0.4"
 arrayref = "0.3.6"
 base64 = "0.13.0"
 bincode = "1.3.1"
-bitcoin = { version = "0.27", features = [ "use-serde" ] }
+bitcoin = { version = "0.26.0", features = [ "use-serde" ] }
 clap = "2.33.3"
 crossbeam-channel = "0.5.0"
 dirs = "3.0.1"
-elements = { version = "0.18", features = [ "serde-feature" ], optional = true }
+elements = { version = "0.16.0", features = [ "serde-feature" ], optional = true }
 error-chain = "0.12.4"
 glob = "0.3"
 hex = "0.4.2"

Cargo.toml

@@ -4,7 +4,6 @@ use std::sync::{Arc, RwLock};
 use bitcoin::hashes::{hex::FromHex, sha256, Hash};
 use elements::confidential::{Asset, Value};
 use elements::encode::{deserialize, serialize};
-use elements::secp256k1_zkp::ZERO_TWEAK;
 use elements::{issuance::ContractHash, AssetId, AssetIssuance, OutPoint, Transaction, TxIn};
 
 use crate::chain::{BNetwork, BlockHash, Network, Txid};
@@ -279,7 +278,7 @@ fn index_tx_assets(
                 }),
             ));
         } else if txi.has_issuance() {
-            let is_reissuance = txi.asset_issuance.asset_blinding_nonce != ZERO_TWEAK;
+            let is_reissuance = txi.asset_issuance.asset_blinding_nonce != [0u8; 32];
 
             let asset_entropy = get_issuance_entropy(txi).expect("invalid issuance");
             let asset_id = AssetId::from_entropy(asset_entropy);
@@ -396,7 +395,7 @@ pub fn get_issuance_entropy(txin: &TxIn) -> Result<sha256::Midstate> {
         bail!("input has no issuance");
     }
 
-    let is_reissuance = txin.asset_issuance.asset_blinding_nonce != ZERO_TWEAK;
+    let is_reissuance = txin.asset_issuance.asset_blinding_nonce != [0u8; 32];
 
     Ok(if !is_reissuance {
         let contract_hash = ContractHash::from_slice(&txin.asset_issuance.asset_entropy)