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.
{
    if (!CCryptoKeyStore::AddWatchOnly(dest))
        return false;
    const CKeyMetadata& meta = mapKeyMetadata[CScriptID(dest)];
    UpdateTimeFirstKey(meta.nCreateTime);
    NotifyWatchonlyChanged(true);
    return CWalletDB(*dbw).WriteWatchOnly(dest, meta);
}
bool CWallet::AddWatchOnly(const CScript& dest, int64_t nCreateTime)
{
    mapKeyMetadata[CScriptID(dest)].nCreateTime = nCreateTime;
    return AddWatchOnly(dest);
}
bool CWallet::RemoveWatchOnly(const CScript &dest)
{
    AssertLockHeld(cs_wallet);
    if (!CCryptoKeyStore::RemoveWatchOnly(dest))
        return false;
    if (!HaveWatchOnly())
        NotifyWatchonlyChanged(false);
    if (!CWalletDB(*dbw).EraseWatchOnly(dest))
        return false;
    return true;
}
bool CWallet::LoadWatchOnly(const CScript &dest)