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.
#include <utility>
#include <vector>
typedef CWallet* CWalletRef;
extern std::vector<CWalletRef> vpwallets;
/**
 * Settings
 */
extern CFeeRate payTxFee;
extern unsigned int nTxConfirmTarget;
extern bool bSpendZeroConfChange;
extern bool fWalletRbf;
static const unsigned int DEFAULT_KEYPOOL_SIZE = 1000;
static const CAmount DEFAULT_TRANSACTION_FEE = 0;
static const CAmount DEFAULT_FALLBACK_FEE = 20000;
static const CAmount DEFAULT_DISCARD_FEE = 10000;
static const CAmount DEFAULT_TRANSACTION_MINFEE = 1000;
static const CAmount WALLET_INCREMENTAL_RELAY_FEE = 5000;
static const CAmount MIN_CHANGE = CENT;
static const CAmount MIN_FINAL_CHANGE = MIN_CHANGE/2;
static const bool DEFAULT_SPEND_ZEROCONF_CHANGE = true;
static const bool DEFAULT_WALLET_REJECT_LONG_CHAINS = false;
static const unsigned int DEFAULT_TX_CONFIRM_TARGET = 6;
static const bool DEFAULT_WALLET_RBF = false;
static const bool DEFAULT_WALLETBROADCAST = true;
static const bool DEFAULT_DISABLE_WALLET = false;
static const bool DEFAULT_USE_HD_WALLET = true;
extern const char * DEFAULT_WALLET_DAT;
static const int64_t TIMESTAMP_MIN = 0;
class CBlockIndex;
class CCoinControl;