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.
{
    if (!EnsureWalletIsAvailable(request.fHelp))
        return NullUniValue;
    if (request.fHelp || request.params.size() != 1)
        throw runtime_error(
            "backupwallet \"destination\"\n"
            "\nSafely copies current wallet file to destination, which can be a directory or a path with filename.\n"
            "\nArguments:\n"
            "1. \"destination\"   (string) The destination directory or file\n"
            "\nExamples:\n"
            + HelpExampleCli("backupwallet", "\"backup.dat\"")
            + HelpExampleRpc("backupwallet", "\"backup.dat\"")
        );
    LOCK2(cs_main, pwalletMain->cs_wallet);
    string strDest = request.params[0].get_str();
    if (!pwalletMain->BackupWallet(strDest))
        throw JSONRPCError(RPC_WALLET_ERROR, "Error: Wallet backup failed!");
    return NullUniValue;
}
UniValue keypoolrefill(const JSONRPCRequest& request)