This change does two things:
- No longer dim display before the dim time set by the user elapses.
  This fixes bug #304696
- No longer assume that 0% display brightness produces a visible result.
  This doesn't work with the intel-backlight backlight interface (as it
  turns off the backlight at 0% brightness). According to the kernel
  developers (see [1] and [2]), this isn't a safe assumption to make for
  other backlight interfaces either. Instead of always dimming to 0%,
  make the amount of dimming configurable.

[1]
http://lists.freedesktop.org/archives/intel-gfx/2013-March/026152.html
[2]
http://lists.freedesktop.org/archives/intel-gfx/2013-March/026140.html