INT 2F - DOS 3.3+ KEYB.COM - SET KEYBOARD CODE PAGE
        AX = AD81h
        BX = code page (see INT 21/AX=6601h)
Return: CF set on error
            AX = 0001h (code page not available)
        CF clear if successful
Notes:  called by DISPLAY.SYS
        undocumented prior to the release of DOS 5.0