INT 21 - DOS 2+ - "SWITCHAR" - GET SWITCH CHARACTER
        AX = 3700h
Return: AL = status
            00h successful
                DL = current switch character
            FFh unsupported subfunction
Desc:   Determine the character which is used to introduce command switches.
          This setting is ignored by DOS commands in version 4.0 and higher,
          but is honored by many third-party programs.
Notes:  documented in some OEM versions of some releases of DOS
        supported by OS/2 compatibility box
        always returns DL=2Fh for DOS 5.0