INT 21 - LANtastic - GET ACTIVE USER INFORMATION
        AX = 5FB0h
        BX = server login entry index
        DS:SI -> buffer for active user entry (see below)
        ES:DI -> ASCIZ machine name in form "\\server"
Return: CF clear if successful
        CF set on error
            AX = error code
        BX = next login index

Format of active user entry:
Offset  Size    Description
 00h    WORD    virtual circuit number
 02h    BYTE    login state
                bit 0: fully logged in
                    1: remote program load login
                    2: user has system manager privileges
                    3: user can create audit entries
                    4: bypass mail protection
                    5: treat as local process
                    6: bypass queue protection
                    7: bypass access control lists
 03h    BYTE    last command issued (see below)
 04h  5 BYTEs   number of I/O bytes (40-bit unsigned number)
 09h  3 BYTEs   number of server requests (24-bit unsigned)
 0Ch 16 BYTEs   name of user who is logged in
 1Ch 16 BYTEs   name of remote logged in machine
 2Ch    BYTE    extended privileges (v4+???)
                bit 0: user cannot change his password
 2Dh    WORD    time left in minutes (0000h = unlimited) (v4+???)

Values for last command:
 00h    login
 01h    process termination
 02h    open file
 03h    close file
 04h    create file
 05h    create new file
 06h    create unique file
 07h    commit data to disk
 08h    read file
 09h    write file
 0Ah    delete file
 0Bh    set file attributes
 0Ch    lock byte range
 0Dh    unlock byte range
 0Eh    create subdirectory
 0Fh    remove subdirectory
 10h    rename file
 11h    find first matching file
 12h    find next matching file
 13h    get disk free space
 14h    get a queue entry
 15h    set a queue entry
 16h    control the queue
 17h    return login information
 18h    return link description
 19h    seek on file
 1Ah    get server's time
 1Bh    create audit entry
 1Ch    open file in multitude of modes
 1Dh    change password
 1Eh    disable account
 1Fh    local server file copy
---v3+---
 20h    get username from account file
 21h    translate server's logical path
 22h    make indirect file
 23h    get indirect file contents
 24h    get physical printer status
 25h    get logical print stream info
 26h    set logical print stream info
 27h    get user's account record
---v4+---
 28h    request server shutdown
 29h    cancel server shutdown
 2Ah    stuff server's keyboard
 2Bh    write then commit data to disk
 2Ch    set extended queue entry
 2Dh    terminate user from server
 2Eh    enable/disable logins
 2Fh    flush server caches
 30h    change username
 31h    get extended queue entry
        (same as get queue, but can return named fields blanked)