INT 2F U - DOS 3.3+ APPEND - GET VERSION INFO
        AX = B710h
Return: AX = current APPEND state (see AX=B706h)
        BX = ??? (0000h in MSDOS 3.30 and 5.00)
        CX = ??? (0000h in MSDOS 3.30 and 5.00)
        DL = major version
        DH = minor version