INT 21 - DOS 2+ - "CHDIR" - SET CURRENT DIRECTORY
        AH = 3Bh
        DS:DX -> ASCIZ pathname to become current directory (max 64 bytes)
Return: CF clear if successful
            AX destroyed
        CF set on error
            AX = error code (03h) (see AH=59h)
Notes:  if new directory name includes a drive letter, the default drive is
          not changed, only the current directory on that drive
        changing the current directory also changes the directory in which
          FCB file calls operate
        under the FlashTek X-32 DOS extender, the pointer is in DS:EDX
SeeAlso: INT 2F/AX=1105h