Use a better default for web root.

This should be use in all the other places, but this was enough for
me to debug the issue at hand.

webv4/root/index.xjs

 <?xjs
-	var settings = load('modopts.js', 'web') || { web_directory: '../webv4' };
+	var settings = load('modopts.js', 'web') || { web_directory: web_root_dir + '/..' };
 	load(settings.web_directory + '/lib/init.js');
 	load(settings.web_lib + 'auth.js');
 	load(settings.web_lib + 'pages.js');