The user of-course can already implicitly work out this information from comparing the fee-rate with the actual fee.

I think that it would be useful for people not wanting to do this arithmetic in their head.

COutPoint(uint256 hashIn, uint32_t nIn) { hash = hashIn; n = nIn; }
    ADD_SERIALIZE_METHODS;
    template <typename Stream, typename Operation>
    inline void SerializationOp(Stream& s, Operation ser_action, int nType, int nVersion) {
        READWRITE(hash);
        READWRITE(n);
    }
    void SetNull() { hash.SetNull(); n = (uint32_t) -1; }
    bool IsNull() const { return (hash.IsNull() && n == (uint32_t) -1); }
    friend bool operator<(const COutPoint& a, const COutPoint& b)
    {
        int cmp = a.hash.Compare(b.hash);
        return cmp < 0 || (cmp == 0 && a.n < b.n);
    }
    friend bool operator==(const COutPoint& a, const COutPoint& b)
    {
        return (a.hash == b.hash && a.n == b.n);
    }
    friend bool operator!=(const COutPoint& a, const COutPoint& b)
    {
        return !(a == b);
    }
    std::string ToString() const;
};
/** An input of a transaction.  It contains the location of the previous
 * transaction's output that it claims and a signature that matches the
 * output's public key.
 */
class CTxIn