When importing a watch-only address over `importmulti` with a specific timestamp, the wallet's `nTimeFirstKey` will be set to 1.
I think we should add a optional timestamp to `CWallet::AddWatchOnly()` and use it when importing addresses or pubkeys.

CWalletDB walletdb(strWalletFile);
    return walletdb.ListAccountCreditDebit(strAccount, entries);
}
bool CWallet::AddAccountingEntry(const CAccountingEntry& acentry)
{
    CWalletDB walletdb(strWalletFile);
    return AddAccountingEntry(acentry, &walletdb);
}
bool CWallet::AddAccountingEntry(const CAccountingEntry& acentry, CWalletDB *pwalletdb)
{
    if (!pwalletdb->WriteAccountingEntry_Backend(acentry))
        return false;
    laccentries.push_back(acentry);
    CAccountingEntry & entry = laccentries.back();
    wtxOrdered.insert(make_pair(entry.nOrderPos, TxPair((CWalletTx*)0, &entry)));
    return true;
}
CAmount CWallet::GetRequiredFee(unsigned int nTxBytes)