[ltp] brightness buttons on T61

[Cherife Li]

As <m h> asked a volume buttons issue on T61p, I'm posting a brightness 
buttons issue on T61 here so won't offing <m h>'s topic.
(I'm wondering whether <m h> has this same issue.)

I recall that some people said in a forum (forgot which), in tty 
console, the brightness buttons do work, but have a bit latency. And you 
need to switch between console and Xwindow to see the effect.
Same here.
Further more, I find that in a certain *short* time after pressed the 
brightness buttons in tty console, then back to Xwindow and pressed the 
buttons, the brightness value changed (in 
/sys/class/backlight/acpi_video1/{actual_brightness,brightness}), but no 
effect. If the *short* time is a bit long, then no changes to acpi.
-- 
Rgds,
Cherife.