Added a hack that removes ugly lines when shadows are enabled.

Mathematically it's not 100% correct, but it looks much better.

data/shaders/sunlightshadow.frag

@@ -35,7 +35,11 @@ float getShadowFactor(vec3 pos, int index)
     for (float i = -1.; i <= 1.; i += 1.)
     {
         for (float j = -1.; j <= 1.; j += 1.)
-            result += texture(shadowtex, vec4(shadowtexcoord + vec2(i,j) / shadow_res, float(index), d));
+        {
+            // result += texture(shadowtex, vec4(shadowtexcoord + vec2(i,j) / shadow_res, float(index), d));
+            // Added a hack with j+1. to avoid ugly lines
+            result += texture(shadowtex, vec4(shadowtexcoord + vec2(i,j+1.) / shadow_res, float(index), d));
+        }
     }
 
     return result / 9.;