Bug#565638: libsdl1.2: SDL_SetGamma() is nonfunctional with xorg 7.5

[nan9]

I've been experiencing this bug, which makes most SDL-based games
unplayable on my system, due to my monitor brightness being too low by
default (adjusting the monitor controls fixes the situation somewhat,
but the colors become weird).

So far, the only workaround that reliably works for me is to launch
the games using the following environment variable:

SDL_VIDEO_X11_NODIRECTCOLOR=1

Using it, the brightness controls work on both Eduke32 and Enigma. In
Eduke32, it affects only the game window, while in Enigma, the entire
screen brightness is changed, just like when using xrandr/xgamma. I
haven't tested other games.

I haven't found any negative side effects, so posting this here in case
someone for whom the patch doesn't work needs a workaround.