If one calls `fundrawtransaction`, the change address will be retrieved from the keypool, though, this key/address will always be returned to the pool, leading to the problem that the next `getnewaddress()` call will restult in the same key/address.

Either we remove the auto-change-address (users would need to call `getrawchangeaddress` first [current best practice anyway]) or we add a call to keep/mark a specific key/address as change (after one have sent the funded raw transaction).

Reported by @NicolasDorier on IRC.
{
    if (pwallet == 0)
        return 0;
    
    if (IsCoinBase() && GetBlocksToMaturity() > 0)
        return 0;
    if (fUseCache && fAvailableCreditCached)
        return nAvailableCreditCached;
    CAmount nCredit = 0;
    uint256 hashTx = GetHash();
    for (unsigned int i = 0; i < tx->vout.size(); i++)
    {
        if (!pwallet->IsSpent(hashTx, i))
        {
            const CTxOut &txout = tx->vout[i];
            nCredit += pwallet->GetCredit(txout, ISMINE_SPENDABLE);
            if (!MoneyRange(nCredit))
                throw std::runtime_error("CWalletTx::GetAvailableCredit() : value out of range");
        }
    }
    nAvailableCreditCached = nCredit;
    fAvailableCreditCached = true;
    return nCredit;
}
CAmount CWalletTx::GetImmatureWatchOnlyCredit(const bool& fUseCache) const