Track and report wallet transaction clones

Adds a "walletconflicts" array to transaction info; if
a wallet transaction is mutated, the alternate transaction id
or ids are reported there (usually the array will be empty).

Metadata from the original transaction is copied to the mutant,
so the transaction time and "from" account of the mutant are
reported correctly.

src/wallet.h

@@ -108,6 +108,12 @@ private:
     int64_t nNextResend;
     int64_t nLastResend;
 
+    // Used to detect and report conflicted transactions:
+    typedef std::multimap<COutPoint, uint256> TxConflicts;
+    TxConflicts mapTxConflicts;
+    void AddToConflicts(const uint256& wtxhash);
+    void SyncMetaData(std::pair<TxConflicts::iterator, TxConflicts::iterator>);
+
 public:
     /// Main wallet lock.
     /// This lock protects all the fields added by CWallet
@@ -151,6 +157,7 @@ public:
     }
 
     std::map<uint256, CWalletTx> mapWallet;
+
     int64_t nOrderPosNext;
     std::map<uint256, int> mapRequestCount;
 
@@ -223,7 +230,7 @@ public:
     TxItems OrderedTxItems(std::list<CAccountingEntry>& acentries, std::string strAccount = "");
 
     void MarkDirty();
-    bool AddToWallet(const CWalletTx& wtxIn);
+    bool AddToWallet(const CWalletTx& wtxIn, bool fFromLoadWallet=false);
     void SyncTransaction(const uint256 &hash, const CTransaction& tx, const CBlock* pblock);
     bool AddToWalletIfInvolvingMe(const uint256 &hash, const CTransaction& tx, const CBlock* pblock, bool fUpdate);
     void EraseFromWallet(const uint256 &hash);
@@ -357,6 +364,9 @@ public:
     // get the current wallet format (the oldest client version guaranteed to understand this wallet)
     int GetVersion() { AssertLockHeld(cs_wallet); return nWalletVersion; }
 
+    // Get wallet transactions that conflict with given transaction (spend same outputs)
+    std::set<uint256> GetConflicts(const uint256& txid) const;
+
     /** Address book entry changed.
      * @note called with lock cs_wallet held.
      */
@@ -752,6 +762,8 @@ public:
     void AddSupportingTransactions();
     bool AcceptWalletTransaction();
     void RelayWalletTransaction();
+
+    std::set<uint256> GetConflicts() const;
 };