Improve ledger replay logic

Build a replay structure holding the transactions
in execution order along with the close time. Use
this structure when replaying a ledger close.

src/ripple/app/ledger/impl/LedgerMaster.cpp

@@ -96,6 +96,9 @@ public:
 
     CanonicalTXSet mHeldTransactions;
 
+    // A set of transactions to replay during the next close
+    std::unique_ptr<LedgerReplay> replayData;
+
     LockType mCompleteLock;
     RangeSet mCompleteLedgers;
 
@@ -1538,6 +1541,16 @@ public:
         mLedgerHistory.clearLedgerCachePrior (seq);
     }
 
+    void takeReplay (std::unique_ptr<LedgerReplay> replay) override
+    {
+        replayData = std::move (replay);
+    }
+
+    std::unique_ptr<LedgerReplay> releaseReplay () override
+    {
+        return std::move (replayData);
+    }
+
     // Fetch packs:
     void gotFetchPack (
         bool progress,