### Describe the issue

Testing in bitcoin 0.13.0, calling `bitcoin-cli listsinceblock x` is outputting all double-spent transactions that are in the wallet, even those that were double-spent well and truly before x.
### Is the issue reproducible?

Yes
#### List steps to reproduce below:
1.   Create a double-spend send to your wallet (easiest using bip125)
2.   Wait until one confirms, and then wait a few more blocks
3.   Run `bitcoin-cli listsinceblock $(bitcoin-cli getbestblockhash)` and it will output the double spent transaction
### Expected behavior

The double-spent transaction that was conflicted before the block hash should be filtered

"\nNow we can do something like sign\n"
            + HelpExampleCli("signmessage", "\"address\" \"test message\"") +
            "\nNow lock the wallet again by removing the passphrase\n"
            + HelpExampleCli("walletlock", "") +
            "\nAs a JSON-RPC call\n"
            + HelpExampleRpc("encryptwallet", "\"my pass phrase\"")
                },
            }.Check(request);
    auto locked_chain = pwallet->chain().lock();
    LOCK(pwallet->cs_wallet);
    if (pwallet->IsWalletFlagSet(WALLET_FLAG_DISABLE_PRIVATE_KEYS)) {
        throw JSONRPCError(RPC_WALLET_ENCRYPTION_FAILED, "Error: wallet does not contain private keys, nothing to encrypt.");
    }
    if (pwallet->IsCrypted()) {
        throw JSONRPCError(RPC_WALLET_WRONG_ENC_STATE, "Error: running with an encrypted wallet, but encryptwallet was called.");
    }
    
    
    SecureString strWalletPass;
    strWalletPass.reserve(100);
    strWalletPass = request.params[0].get_str().c_str();
    if (strWalletPass.empty()) {
        throw JSONRPCError(RPC_INVALID_PARAMETER, "passphrase can not be empty");
    }
    if (!pwallet->EncryptWallet(strWalletPass)) {
        throw JSONRPCError(RPC_WALLET_ENCRYPTION_FAILED, "Error: Failed to encrypt the wallet.");
    }
    return "wallet encrypted; The keypool has been flushed and a new HD seed was generated (if you are using HD). You need to make a new backup.";
}
static UniValue lockunspent(const JSONRPCRequest& request)