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.
{
    nIndex = -1;
    keypool.vchPubKey = CPubKey();
    {
        LOCK(cs_wallet);
        if (!IsLocked())
            TopUpKeyPool();
        
        if(setKeyPool.empty())
            return;
        CWalletDB walletdb(strWalletFile);
        nIndex = *(setKeyPool.begin());
        setKeyPool.erase(setKeyPool.begin());
        if (!walletdb.ReadPool(nIndex, keypool))
            throw runtime_error(std::string(__func__) + ": read failed");
        if (!HaveKey(keypool.vchPubKey.GetID()))
            throw runtime_error(std::string(__func__) + ": unknown key in key pool");
        assert(keypool.vchPubKey.IsValid());
        LogPrintf("keypool reserve %d\n", nIndex);
    }
}
void CWallet::KeepKey(int64_t nIndex)