Merge branch 'master' into jgrpp

# Conflicts:
#	src/aircraft_cmd.cpp
#	src/autoreplace_cmd.cpp
#	src/pathfinder/follow_track.hpp
#	src/pathfinder/yapf/yapf_rail.cpp
#	src/saveload/afterload.cpp
#	src/saveload/saveload.cpp
#	src/script/api/ai/ai_station.hpp.sq
#	src/script/api/game/game_station.hpp.sq
#	src/script/api/script_station.hpp
#	src/track_func.h
#	src/vehicle_base.h

src/script/api/script_airport.cpp

@@ -163,3 +163,10 @@
 
 	return AirportSpec::Get(type)->maintenance_cost;
 }
+
+/* static */ Money ScriptAirport::GetMonthlyMaintenanceCost(AirportType type)
+{
+	if (!IsAirportInformationAvailable(type)) return -1;
+
+	return (int64)GetMaintenanceCostFactor(type) * _price[PR_INFRASTRUCTURE_AIRPORT] >> 3;
+}