Merge branch 'master' into jgrpp

# Conflicts:
#	regression/regression/result.txt
#	src/aircraft_cmd.cpp
#	src/airport_gui.cpp
#	src/articulated_vehicles.cpp
#	src/console_cmds.cpp
#	src/date_gui.cpp
#	src/engine.cpp
#	src/genworld_gui.cpp
#	src/gfx_layout_fallback.cpp
#	src/group_gui.cpp
#	src/hotkeys.cpp
#	src/network/core/tcp_connect.cpp
#	src/network/core/tcp_listen.h
#	src/newgrf.cpp
#	src/newgrf.h
#	src/newgrf_engine.cpp
#	src/newgrf_gui.cpp
#	src/newgrf_station.cpp
#	src/openttd.cpp
#	src/order_gui.cpp
#	src/os/macosx/osx_main.cpp
#	src/pathfinder/yapf/yapf_node_rail.hpp
#	src/rail_gui.cpp
#	src/saveload/afterload.cpp
#	src/saveload/cargopacket_sl.cpp
#	src/saveload/linkgraph_sl.cpp
#	src/saveload/station_sl.cpp
#	src/script/api/script_industrytype.cpp
#	src/settings.cpp
#	src/settings_gui.cpp
#	src/settings_table.cpp
#	src/settingsgen/settingsgen.cpp
#	src/station.cpp
#	src/station_cmd.cpp
#	src/strings.cpp
#	src/timer/timer_game_calendar.cpp
#	src/timer/timer_game_calendar.h
#	src/timer/timer_manager.h
#	src/timer/timer_window.cpp
#	src/timetable_cmd.cpp
#	src/toolbar_gui.cpp
#	src/town_cmd.cpp
#	src/town_gui.cpp
#	src/train_gui.cpp
#	src/vehicle_cmd.h
#	src/vehicle_gui.cpp
#	src/viewport.cpp
#	src/widgets/dropdown.cpp
#	src/window_func.h
#	src/window_gui.h

src/engine.cpp

@@ -486,7 +486,8 @@ uint Engine::GetDisplayMaxTractiveEffort() const
  */
 Date Engine::GetLifeLengthInDays() const
 {
-	return DateAtStartOfYear(this->info.lifelength + _settings_game.vehicle.extend_vehicle_life);
+	/* Assume leap years; this gives the player a bit more than the given amount of years, but never less. */
+	return static_cast<int32_t>(this->info.lifelength + _settings_game.vehicle.extend_vehicle_life) * DAYS_IN_LEAP_YEAR;
 }
 
 /**
@@ -539,7 +540,7 @@ bool Engine::IsVariantHidden(CompanyID c) const
 	 * the last display variant rather than the actual parent variant. */
 	const Engine *re = this;
 	const Engine *ve = re->GetDisplayVariant();
-	while (!(ve->IsHidden(c)) && re->info.variant_id != INVALID_ENGINE && re->info.variant_id != re->index) {
+	while (!(ve->IsHidden(c)) && re->info.variant_id != INVALID_ENGINE) {
 		re = Engine::Get(re->info.variant_id);
 		ve = re->GetDisplayVariant();
 	}
@@ -668,7 +669,7 @@ void CalcEngineReliability(Engine *e, bool new_month)
 {
 	/* Get source engine for reliability age. This is normally our engine unless variant reliability syncing is requested. */
 	Engine *re = e;
-	while (re->info.variant_id != INVALID_ENGINE && re->info.variant_id != re->index && (re->info.extra_flags & ExtraEngineFlags::SyncReliability) != ExtraEngineFlags::None) {
+	while (re->info.variant_id != INVALID_ENGINE && (re->info.extra_flags & ExtraEngineFlags::SyncReliability) != ExtraEngineFlags::None) {
 		re = Engine::Get(re->info.variant_id);
 	}
 
@@ -725,7 +726,7 @@ void SetYearEngineAgingStops()
 
 		/* Base year ending date on half the model life */
 		YearMonthDay ymd;
-		ConvertDateToYMD(ei->base_intro + DateAtStartOfYear(ei->lifelength) / 2, &ymd);
+		ConvertDateToYMD(ei->base_intro + (static_cast<int32_t>(ei->lifelength) * DAYS_IN_LEAP_YEAR) / 2, &ymd);
 
 		_year_engine_aging_stops = std::max(_year_engine_aging_stops, ymd.year);
 	}
@@ -768,7 +769,7 @@ void StartupOneEngine(Engine *e, Date aging_date, uint32 seed, Date no_introduce
 
 	/* Get parent variant index for syncing reliability via random seed. */
 	const Engine *re = e;
-	while (re->info.variant_id != INVALID_ENGINE && re->info.variant_id != re->index && (re->info.extra_flags & ExtraEngineFlags::SyncReliability) != ExtraEngineFlags::None) {
+	while (re->info.variant_id != INVALID_ENGINE && (re->info.extra_flags & ExtraEngineFlags::SyncReliability) != ExtraEngineFlags::None) {
 		re = Engine::Get(re->info.variant_id);
 	}