(svn r13226) -Feature: Allow to have more than only two airports per town. The number of airports is now controlled by the noise each of them generates, the distance from town's center and how tolerant the town is.

Initial concept : TTDPatch (moreairpots),  Initial code : Pasky
Thanks to BigBB (help coding), Smatz Skidd13 and frosch for bugcatches and advices

src/settings_type.h

@@ -10,7 +10,27 @@
 #include "town_type.h"
 #include "transport_type.h"
 
-#define GAME_DIFFICULTY_NUM 18
+enum {
+	GAME_DIFFICULTY_AI_NUMBER,
+	GAME_DIFFICULTY_AI_STARTTIME,
+	GAME_DIFFICULTY_TOWN_NUMBER,
+	GAME_DIFFICULTY_INDUSTRIE_NUMBER,
+	GAME_DIFFICULTY_MAX_LOAN,
+	GAME_DIFFICULTY_INITIAL_INTEREST,
+	GAME_DIFFICULTY_VEHICLE_COST,
+	GAME_DIFFICULTY_AI_SPEED,
+	GAME_DIFFICULTY_AI_INTELLIGENCE, ///< no longer in use
+	GAME_DIFFICULTY_VEHICLES_BREAKDOWN,
+	GAME_DIFFICULTY_SUBSIDY_MULTIPLIER,
+	GAME_DIFFICULTY_CONSTRUCTION_COST,
+	GAME_DIFFICULTY_TYPE_TERRAIN,
+	GAME_DIFFICULTY_SEALAKE_NUMBER,
+	GAME_DIFFICULTY_ECONOMY,
+	GAME_DIFFICULTY_LINE_REVERSEMODE,
+	GAME_DIFFICULTY_DISASTERS,
+	GAME_DIFFICULTY_TOWNCOUNCIL_TOLERANCE, ///< minimum required town ratings to be allowed to demolish stuff
+	GAME_DIFFICULTY_NUM,
+};
 
 /** Specific type for Game Difficulty to ease changing the type */
 typedef uint16 GDType;
@@ -221,6 +241,8 @@ struct Patches {
 	bool pause_on_newgame;       ///< Whether to start new games paused or not.
 
 	TownLayoutByte town_layout;  ///< Select town layout
+	bool station_noise_level;        ///< build new airports when the town noise level is still within accepted limits
+	uint16 town_noise_population[3];  ///< Population to base decision on noise evaluation (@see town_council_tolerance)
 
 	bool timetabling;            ///< Whether to allow timetabling.
 	bool timetable_in_ticks;     ///< Whether to show the timetable in ticks rather than days.