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.

}
    }
    return balances;
}
set< set<CTxDestination> > CWallet::GetAddressGroupings()
{
    AssertLockHeld(cs_wallet); 
    set< set<CTxDestination> > groupings;
    set<CTxDestination> grouping;
    BOOST_FOREACH(PAIRTYPE(uint256, CWalletTx) walletEntry, mapWallet)
    {
        CWalletTx *pcoin = &walletEntry.second;
        if (pcoin->tx->vin.size() > 0)
        {
            bool any_mine = false;
            
            BOOST_FOREACH(CTxIn txin, pcoin->tx->vin)
            {
                CTxDestination address;
                if(!IsMine(txin)) 
                    continue;
                if(!ExtractDestination(mapWallet[txin.prevout.hash].tx->vout[txin.prevout.n].scriptPubKey, address))
                    continue;
                grouping.insert(address);
                any_mine = true;
            }
            
            if (any_mine)
            {
               BOOST_FOREACH(CTxOut txout, pcoin->tx->vout)