Don't scale shadow multipliers by overbrightbits, and improve documentation.

code/renderergl2/tr_bsp.c

@@ -3277,7 +3277,8 @@ void RE_LoadWorldMap( const char *name ) {
 	}
 
 	// set default map light scale
-	tr.mapLightScale = 1.0f;
+	tr.mapLightScale  = 1.0f;
+	tr.sunShadowScale = 0.5f;
 
 	// set default sun direction to be used if it isn't
 	// overridden by a shader