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 (nIndex == -1)
    {
        CKeyPool keypool;
        pwallet->ReserveKeyFromKeyPool(nIndex, keypool);
        if (nIndex != -1)
            vchPubKey = keypool.vchPubKey;
        else {
            return false;
        }
    }
    assert(vchPubKey.IsValid());
    pubkey = vchPubKey;
    return true;
}
void CReserveKey::KeepKey()
{
    if (nIndex != -1)
        pwallet->KeepKey(nIndex);
    nIndex = -1;
    vchPubKey = CPubKey();
}
void CReserveKey::ReturnKey()