INT 2A,3 - Check if Direct I/O Allowed

AH = 03

DS:SI = pointer to ASCIIZ disk device name or pathname (including ":")

on return:

CF = set if disk access is NOT allowed

= clear if disk access is allowed

- do not use ~INT 13~, ~INT 25~ or ~INT 26~ if this function returns

with the CF set

- see ~INT 5F,2~