INT 2F U - DOS 4+ internal - GET OR SET ERROR TABLE ADDRESSES
        AX = 122Eh
        DL = subfunction
            00h get standard DOS error table
                Return: ES:DI -> error table
                                 (DOS 4: errors 00h-12h,50h-5Bh)
                                 (DOS 5: errors 00h-26h,4Fh,51h-59h)
            01h set standard DOS error table
                ES:DI -> error table
            02h get parameter error table (errors 00h-0Ah)
                Return: ES:DI -> error table
            03h set parameter error table
                ES:DI -> error table
            04h get critical/SHARE error table (errors 13h-2Bh)
                Return: ES:DI -> error table
            05h set critical/SHARE error table
                ES:DI -> error table
            06h get ??? error table
                Return: ES:DI -> error table or 0000h:0000h
            07h set ??? error table
                ES:DI -> error table
            08h get error message retriever (see below)
                Return: ES:DI -> FAR procedure to fetch error message
            09h set ??? error table
                ES:DI -> error table
Notes:  if the returned segment on a "get" is 0001h, then the offset specifies
          the offset of the error message table within COMMAND.COM, and the
          procedure returned by DL=08h should be called
        DOS 5.0 COMMAND.COM does not allow setting any of the addresses (calls
          with DL odd are ignored); they are always returned with segment 0001h
        for DOS 5.0, the standard and critical/SHARE error tables are combined
          into a single error table
SeeAlso: INT 21/AH=59h

Format of DOS 4.x error table:
Offset  Size    Description
 00h    BYTE    FFh
 01h  2 BYTEs   04h,00h (DOS version???)
 03h    BYTE    number of error headers following
 04h 2N WORDs   table of all error headers for table
                Offset  Size    Description
                 00h    WORD    error message number
                 02h    WORD    offset of error message from start of header
                                error messages are count byte followed by msg
Note:   DOS 5 error tables consist of one word per error number; each word
          contains either the offset of a counted string or 0000h

Call error retrieval function with:
        AX = error number
        DI = offset of error table
Return: ES:DI -> error message (counted string)
Notes:  this function needs to access COMMAND.COM if the messages were not
          loaded into memory permanently with /MSG; the caller should assume
          that the returned message will be overwritten by the next call of
          the function
        supported by DR-DOS 5.0