Built against `master` branch 801dd40666d1e6009920ad3ff755c7bb993b2a62:

If I have no wallet.dat file and run:

    bitcoind -usehd=0

A new wallet.dat file is created and an HD seed is assigned.

I see an error message in the source:

    "Error loading %s: You can't disable HD on an already existing HD wallet or create new non-HD wallets."

but that doesn't get shown because `fFirstRun` is true, and so the code which checks for `-usehd` values doesn't run.

If it's no longer possible to create non-HD wallets, specifying -usehd=0 when creating a wallet should be an error, and not get silently ignored.
{
    CAmount nCredit = 0;
    for (const CTxOut& txout : tx.vout)
    {
        nCredit += GetCredit(txout, filter);
        if (!MoneyRange(nCredit))
            throw std::runtime_error(std::string(__func__) + ": value out of range");
    }
    return nCredit;
}
CAmount CWallet::GetChange(const CTransaction& tx) const
{
    CAmount nChange = 0;
    for (const CTxOut& txout : tx.vout)
    {
        nChange += GetChange(txout);
        if (!MoneyRange(nChange))
            throw std::runtime_error(std::string(__func__) + ": value out of range");
    }
    return nChange;
}
CPubKey CWallet::GenerateNewHDMasterKey()