INT 2F U - DOS 3+ internal - CANONICALIZE FILE NAME
        AX = 1221h
        DS:SI -> file name to be fully qualified
        ES:DI -> 128-byte buffer for resulting canonical file name
        SS = DOS DS (must be using a DOS internal stack)
Return: (see INT 21/AH=60h)
Note:   identical to INT 21/AH=60h
SeeAlso: INT 21/AH=60h