use r_ignorehwgamma cvar to allow user to disable gamma correction

code/unix/sdl_glimp.c

@@ -442,7 +442,12 @@ void GLimp_SetGamma( unsigned char red[256], unsigned char green[256], unsigned
 {
   // NOTE TTimo we get the gamma value from cvar, because we can't work with the s_gammatable
   //   the API wasn't changed to avoid breaking other OSes
-  float g = Cvar_Get("r_gamma", "1.0", 0)->value;
+  float g;
+
+  if ( r_ignorehwgamma->integer )
+    return;
+
+  g  = Cvar_Get("r_gamma", "1.0", 0)->value;
   SDL_SetGamma(g, g, g);
 }
 
@@ -1450,3 +1455,4 @@ void IN_JoyMove( void )
 // end of linux_glimp_sdl.c ...
 
 
+