Add TxPriority class and comparator

Author: morcos

src/txmempool.h

@@ -587,4 +587,17 @@ class CCoinsViewMemPool : public CCoinsViewBacked
     bool HaveCoins(const uint256 &txid) const;
 };
 
+// We want to sort transactions by coin age priority
+typedef std::pair<double, CTxMemPool::txiter> TxCoinAgePriority;
+
+struct TxCoinAgePriorityCompare
+{
+    bool operator()(const TxCoinAgePriority& a, const TxCoinAgePriority& b)
+    {
+        if (a.first == b.first)
+            return CompareTxMemPoolEntryByScore()(*(b.second), *(a.second)); //Reverse order to make sort less than
+        return a.first < b.first;
+    }
+};
+
 #endif // BITCOIN_TXMEMPOOL_H