Update to OpenTTD 1.9.0-beta2

--HG--
branch : openttd

src/script/api/ai_changelog.hpp

@@ -1,4 +1,4 @@
-/* $Id: ai_changelog.hpp 27996 2018-03-21 19:39:49Z frosch $ */
+/* $Id$ */
 
 /*
  * This file is part of OpenTTD.
@@ -15,6 +15,15 @@
  * functions may still be available if you return an older API version
  * in GetAPIVersion() in info.nut.
  *
+ * \b 1.9.0
+ *
+ * 1.9.0 is not yet released. The following changes are not set in stone yet.
+ * API additions:
+ * \li AIAirport::GetMonthlyMaintenanceCost
+ *
+ * Other changes:
+ * \li AIBridge::GetName takes one extra parameter to refer the vehicle type
+ *
  * \b 1.8.0
  *
  * No changes