If one calls `fundrawtransaction`, the change address will be retrieved from the keypool, though, this key/address will always be returned to the pool, leading to the problem that the next `getnewaddress()` call will restult in the same key/address.

Either we remove the auto-change-address (users would need to call `getrawchangeaddress` first [current best practice anyway]) or we add a call to keep/mark a specific key/address as change (after one have sent the funded raw transaction).

Reported by @NicolasDorier on IRC.
payTxFee = CFeeRate(nFeePerK, 1000);
        if (payTxFee < ::minRelayTxFee)
        {
            return InitError(strprintf(_("Invalid amount for -paytxfee=<amount>: '%s' (must be at least %s)"),
                                       GetArg("-paytxfee", ""), ::minRelayTxFee.ToString()));
        }
    }
    if (IsArgSet("-maxtxfee"))
    {
        CAmount nMaxFee = 0;
        if (!ParseMoney(GetArg("-maxtxfee", ""), nMaxFee))
            return InitError(AmountErrMsg("maxtxfee", GetArg("-maxtxfee", "")));
        if (nMaxFee > HIGH_MAX_TX_FEE)
            InitWarning(_("-maxtxfee is set very high! Fees this large could be paid on a single transaction."));
        maxTxFee = nMaxFee;
        if (CFeeRate(maxTxFee, 1000) < ::minRelayTxFee)
        {
            return InitError(strprintf(_("Invalid amount for -maxtxfee=<amount>: '%s' (must be at least the minrelay fee of %s to prevent stuck transactions)"),
                                       GetArg("-maxtxfee", ""), ::minRelayTxFee.ToString()));
        }
    }
    nTxConfirmTarget = GetArg("-txconfirmtarget", DEFAULT_TX_CONFIRM_TARGET);
    bSpendZeroConfChange = GetBoolArg("-spendzeroconfchange", DEFAULT_SPEND_ZEROCONF_CHANGE);
    fSendFreeTransactions = GetBoolArg("-sendfreetransactions", DEFAULT_SEND_FREE_TRANSACTIONS);
    fWalletRbf = GetBoolArg("-walletrbf", DEFAULT_WALLET_RBF);
    if (fSendFreeTransactions && GetArg("-limitfreerelay", DEFAULT_LIMITFREERELAY) <= 0)
        return InitError("Creation of free transactions with their relay disabled is not supported.");
    return true;
}
bool CWallet::BackupWallet(const std::string& strDest)