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.
bool LoadCryptedKey(const CPubKey &vchPubKey, const std::vector<unsigned char> &vchCryptedSecret);
    bool AddCScript(const CScript& redeemScript) override;
    bool LoadCScript(const CScript& redeemScript);
    
    bool AddDestData(const CTxDestination &dest, const std::string &key, const std::string &value);
    
    bool EraseDestData(const CTxDestination &dest, const std::string &key);
    
    bool LoadDestData(const CTxDestination &dest, const std::string &key, const std::string &value);
    
    bool GetDestData(const CTxDestination &dest, const std::string &key, std::string *value) const;
    
    std::vector<std::string> GetDestValues(const std::string& prefix) const;
    
    bool AddWatchOnly(const CScript& dest, int64_t nCreateTime);
    bool RemoveWatchOnly(const CScript &dest) override;
    
    bool LoadWatchOnly(const CScript &dest);
    
    int64_t nRelockTime;
    bool Unlock(const SecureString& strWalletPassphrase);
    bool ChangeWalletPassphrase(const SecureString& strOldWalletPassphrase, const SecureString& strNewWalletPassphrase);
    bool EncryptWallet(const SecureString& strWalletPassphrase);
    void GetKeyBirthTimes(std::map<CTxDestination, int64_t> &mapKeyBirth) const;
    unsigned int ComputeTimeSmart(const CWalletTx& wtx) const;
    /** 
     * Increment the next transaction order id
     * @return next transaction order id
     */