Function 2Bh            Set Date

    Sets the current DOS system date (the date maintained by the clock
    device).

        Entry   AH = 2Bh
                CX = Year (1980 - 2099)
                DH = Month (1 - 12)
                DL = Day (1 - 31)

        Return  AL = 00h   If valid date specified
                AL = FFh   Invalid date, system date unchanged