Fix build with boost 1.87; from FreeBSD

Index: apps/openmw/mwstate/charactermanager.hpp
--- apps/openmw/mwstate/charactermanager.hpp.orig
+++ apps/openmw/mwstate/charactermanager.hpp
@@ -1,6 +1,8 @@
 #ifndef GAME_STATE_CHARACTERMANAGER_H
 #define GAME_STATE_CHARACTERMANAGER_H
 
+#include <list>
+
 #include <boost/filesystem/path.hpp>
 
 #include "character.hpp"
