Update license headers for AMXX core.

amxmodx/messages.cpp

@@ -1,3 +1,12 @@
+// vim: set ts=4 sw=4 tw=99 noet:
+//
+// AMX Mod X, based on AMX Mod by Aleksander Naszko ("OLO").
+// Copyright (C) The AMX Mod X Development Team.
+//
+// This software is licensed under the GNU General Public License, version 3 or higher.
+// Additional exceptions apply. For full license details, see LICENSE.txt or visit:
+//     https://alliedmods.net/amxmodx-license
+
 #include "amxmodx.h"
 #include "messages.h"