- split up g_visibility into two variables.

This is preparation for experimenting with the weapon flashes that can be quite annoying with how they brighten distant parts of the level far more than nearby parts.

source/core/savegamehelp.cpp

@@ -695,6 +695,7 @@ void SerializeMap(FSerializer& arc)
 			("randomseed", randomseed)
 			("numshades", numshades)	// is this really needed?
 			("visibility", g_visibility)
+			("relvisibility", g_relvisibility)
 			("parallaxtype", parallaxtype)
 			("parallaxyo", parallaxyoffs_override)
 			("parallaxys", parallaxyscale_override)