Return Timelocked instead of (Timelock, Vec<SpendableOutput>)

Timelocked doesn't expose the Vec yet requires calling not_locked(), 
unlocked(Timelock), or ignore_timelock().

coins/monero/src/transaction.rs

@@ -1,3 +1,5 @@
+use core::cmp::Ordering;
+
 use curve25519_dalek::edwards::EdwardsPoint;
 
 use crate::{hash, serialize::*, ringct::{RctPrunable, RctSignatures}};
@@ -131,6 +133,17 @@ impl Timelock {
   }
 }
 
+impl PartialOrd for Timelock {
+  fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+    match (self, other) {
+      (Timelock::None, _) => Some(Ordering::Less),
+      (Timelock::Block(a), Timelock::Block(b)) => a.partial_cmp(b),
+      (Timelock::Time(a), Timelock::Time(b)) => a.partial_cmp(b),
+      _ => None
+    }
+  }
+}
+
 #[derive(Clone, PartialEq, Debug)]
 pub struct TransactionPrefix {
   pub version: u64,