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.
{
        SetTx(MakeTransactionRef());
        Init();
    }
    CMerkleTx(CTransactionRef arg)
    {
        SetTx(std::move(arg));
        Init();
    }
    /** Helper conversion operator to allow passing CMerkleTx where CTransaction is expected.
     *  TODO: adapt callers and remove this operator. */
    operator const CTransaction&() const { return *tx; }
    void Init()
    {
        hashBlock = uint256();
        nIndex = -1;
    }
    void SetTx(CTransactionRef arg)
    {
        tx = std::move(arg);
    }
    ADD_SERIALIZE_METHODS;
    template <typename Stream, typename Operation>
    inline void SerializationOp(Stream& s, Operation ser_action) {