Backlight control doesn't work on Dell Vostro 3560

Hello,

I want to report a bug (propably regression) - controlling the LCD backlight through Fn+F4/F5 keys doesn't work.
This is almost certainly the same issue that was mentioned in this
thread: http://www.spinics.net/lists/linux-acpi/msg40404.html

I can confirm it worked on vanilla 3.6.8 and debian 3.2 kernels. It doesn't work on 3.7 or 3.8-rc kernels.

If I should provide any new information not present in the mentioned thread (or repost it), please tell me to do so.

Thanks,
Adrian