INT 2F - AVATAR.SYS - INSTALLATION CHECK
        AX = 1A00h
        BX = 4156h ('AV')
        CX = 4154h ('AT')
        DX = 4152h ('AR')
Return: AL = FFh if installed
            CF clear
            BX = AVATAR protocol level supported
            CX = driver type
                0000h AVATAR.SYS
                4456h DVAVATAR.COM inside DESQview window
            DX = 0016h
Notes:  AVATAR also identifies itself as ANSI.SYS if BX, CX, or DX differ from
          the magic values
        AVATAR.SYS is a CON replacement by George Adam Stanislav which
          interprets AVATAR command codes in the same way that ANSI interprets
          ANSI command codes