INT 21 - DOS 2+ - "MKDIR" - CREATE SUBDIRECTORY
        AH = 39h
        DS:DX -> ASCIZ pathname
Return: CF clear if successful
            AX destroyed
        CF set on error
            AX = error code (03h,05h) (see AH=59h)
Notes:  all directories in the given path except the last must exist
        fails if the parent directory is the root and is full
        DOS 2.x-3.3 allow the creation of a directory sufficiently deep that
          it is not possible to make that directory the current directory
          because the path would exceed 64 characters
        under the FlashTek X-32 DOS extender, the pointer is in DS:EDX
SeeAlso: AH=3Ah,AH=3Bh,AH=6Dh,AH=E2h/SF=0Ah,INT 2F/AX=1103h

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