Implement CTransaction::IsEquivalentTo(...)

Define CTransaction::IsEquivalentTo(const CTransaction& tx)

True if only scriptSigs are different.  In other words, true if
the two transactions are malleability clones.  In other words,
true if the two transactions have the same effect on the
outside universe.

In the wallet, only SyncMetaData for equivalent transactions.

src/wallet/wallet.cpp

@@ -417,6 +417,7 @@ void CWallet::SyncMetaData(pair<TxSpends::iterator, TxSpends::iterator> range)
         const uint256& hash = it->second;
         CWalletTx* copyTo = &mapWallet[hash];
         if (copyFrom == copyTo) continue;
+        if (!copyFrom->IsEquivalentTo(*copyTo)) continue;
         copyTo->mapValue = copyFrom->mapValue;
         copyTo->vOrderForm = copyFrom->vOrderForm;
         // fTimeReceivedIsTxTime not copied on purpose