INT 21 - DOS 4+ - EXTENDED OPEN/CREATE
        AX = 6C00h
        BL = open mode as in AL for normal open (see INT 21/AH=3Dh)
            bit 7: inheritance
            bits 4-6: sharing mode
            bit 3 reserved
            bits 0-2: access mode
        BH = flags
            bit 6 = auto commit on every write (see also AH=68h)
            bit 5 = return error rather than doing INT 24h
        CX = create attribute
            bits 6-15 reserved
            bit 5: archive
            bit 4: reserved
            bit 3: volume label
            bit 2: system
            bit 1: hidden
            bit 0: readonly
        DL = action if file exists/does not exist
            bits 7-4 action if file does not exist
                    0000 fail
                    0001 create
            bits 3-0 action if file exists
                    0000 fail
                    0001 open
                    0010 replace/open
        DH = 00h (reserved)
        DS:SI -> ASCIZ file name
Return: CF set on error
           AX = error code (see AH=59h)
        CF clear if successful
           AX = file handle
           CX = status
                1 file opened
                2 file created
                3 file replaced
Note:   the PC LAN Program only supports DL=01h, DL=10h/sharing=compatibility,
          and DL=12h
SeeAlso: AH=3Ch,AH=3Dh,AX=6C01h

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