Xash3D - gamma fix file

Download and extract xash.dll into Xash3D root directory.
Launch Xash3D with "-console" parameter, and then in console set gamma 2.5, brightness 1.2
Picture should look just like it was in Goldsource.
Enjoy

Code changes:

- In common.h set texgamma to 0.655 (found experimentally, although Goldsource seem to use 0.666 but it doesn't exactly look the same)

-in Image_SetPalette wrap 3 texture channels of LUMP_NORMAL into TextureToGamma(). Just wrap, it's expecting 1 parameter.

-In BuildGammaTable() set g3 = 0.125 unconditionally.

Tested on Xash3D build 4529