Use last_id instead of seed

It doesn't really matter, but was confusing since the seed points
to an entry before the mint's deposit.

src/accountant.rs

@@ -202,11 +202,11 @@ mod tests {
         let alice = Mint::new(10_000);
         let bob_pubkey = KeyPair::new().pubkey();
         let mut acc = Accountant::new(&alice);
-        acc.transfer(1_000, &alice.keypair(), bob_pubkey, alice.seed())
+        acc.transfer(1_000, &alice.keypair(), bob_pubkey, alice.last_id())
             .unwrap();
         assert_eq!(acc.get_balance(&bob_pubkey).unwrap(), 1_000);
 
-        acc.transfer(500, &alice.keypair(), bob_pubkey, alice.seed())
+        acc.transfer(500, &alice.keypair(), bob_pubkey, alice.last_id())
             .unwrap();
         assert_eq!(acc.get_balance(&bob_pubkey).unwrap(), 1_500);
     }
@@ -216,10 +216,10 @@ mod tests {
         let alice = Mint::new(11_000);
         let mut acc = Accountant::new(&alice);
         let bob_pubkey = KeyPair::new().pubkey();
-        acc.transfer(1_000, &alice.keypair(), bob_pubkey, alice.seed())
+        acc.transfer(1_000, &alice.keypair(), bob_pubkey, alice.last_id())
             .unwrap();
         assert_eq!(
-            acc.transfer(10_001, &alice.keypair(), bob_pubkey, alice.seed()),
+            acc.transfer(10_001, &alice.keypair(), bob_pubkey, alice.last_id()),
             Err(AccountingError::InsufficientFunds)
         );
 
@@ -233,7 +233,7 @@ mod tests {
         let alice = Mint::new(1);
         let mut acc = Accountant::new(&alice);
         let bob_pubkey = KeyPair::new().pubkey();
-        let mut tr = Transaction::new(&alice.keypair(), bob_pubkey, 1, alice.seed());
+        let mut tr = Transaction::new(&alice.keypair(), bob_pubkey, 1, alice.last_id());
         if let Plan::Pay(ref mut payment) = tr.plan {
             payment.tokens = 2; // <-- attack!
         }
@@ -258,7 +258,7 @@ mod tests {
         let mut acc = Accountant::new(&alice);
         let alice_keypair = alice.keypair();
         let bob_pubkey = KeyPair::new().pubkey();
-        acc.transfer(500, &alice_keypair, bob_pubkey, alice.seed())
+        acc.transfer(500, &alice_keypair, bob_pubkey, alice.last_id())
             .unwrap();
         assert_eq!(acc.get_balance(&bob_pubkey).unwrap(), 500);
     }
@@ -270,7 +270,7 @@ mod tests {
         let alice_keypair = alice.keypair();
         let bob_pubkey = KeyPair::new().pubkey();
         let dt = Utc::now();
-        acc.transfer_on_date(1, &alice_keypair, bob_pubkey, dt, alice.seed())
+        acc.transfer_on_date(1, &alice_keypair, bob_pubkey, dt, alice.last_id())
             .unwrap();
 
         // Alice's balance will be zero because all funds are locked up.
@@ -299,7 +299,7 @@ mod tests {
         acc.process_verified_timestamp(alice.pubkey(), dt).unwrap();
 
         // It's now past now, so this transfer should be processed immediately.
-        acc.transfer_on_date(1, &alice_keypair, bob_pubkey, dt, alice.seed())
+        acc.transfer_on_date(1, &alice_keypair, bob_pubkey, dt, alice.last_id())
             .unwrap();
 
         assert_eq!(acc.get_balance(&alice.pubkey()), Some(0));
@@ -313,7 +313,7 @@ mod tests {
         let alice_keypair = alice.keypair();
         let bob_pubkey = KeyPair::new().pubkey();
         let dt = Utc::now();
-        let sig = acc.transfer_on_date(1, &alice_keypair, bob_pubkey, dt, alice.seed())
+        let sig = acc.transfer_on_date(1, &alice_keypair, bob_pubkey, dt, alice.last_id())
             .unwrap();
 
         // Alice's balance will be zero because all funds are locked up.

src/accountant_stub.rs

@@ -106,10 +106,10 @@ mod tests {
         let acc = Accountant::new(&alice);
         let bob_pubkey = KeyPair::new().pubkey();
         let exit = Arc::new(AtomicBool::new(false));
-        let historian = Historian::new(&alice.seed(), Some(30));
+        let historian = Historian::new(&alice.last_id(), Some(30));
         let acc = Arc::new(Mutex::new(AccountantSkel::new(
             acc,
-            alice.seed(),
+            alice.last_id(),
             sink(),
             historian,
         )));

src/mint.rs

@@ -33,6 +33,10 @@ impl Mint {
         hash(&self.pkcs8)
     }
 
+    pub fn last_id(&self) -> Hash {
+        self.create_entries()[1].id
+    }
+
     pub fn keypair(&self) -> KeyPair {
         KeyPair::from_pkcs8(Input::from(&self.pkcs8)).unwrap()
     }