(svn r5946) -Add: merged the TGP branch to mainline. TGP adds:

- New optional landscape generator (TerraGenesis Perlin)
  - Load heightmaps (either BMP or PNG)
  - Progress dialog while generating worlds (no longer a 'hanging' screen)
  - New dialogs for NewGame, Create Scenario and Play Heightmap
    - Easier to configure your landscape
    - More things to configure (tree-placer, ..)
  - Speedup of world generation
  - New console command 'restart': restart the map EXACTLY as it was when you
      first started it (needs a game made after or with this commit)
  - New console command 'getseed': get the seed of your map and share it with
      others (of course only works with generated maps)
  - Many new, world generation related, things
  - Many internal cleanups and rewrites
  Many tnx to those people who helped making this:
     Belugas, DaleStan, glx, KUDr, RichK67, Rubidium, and TrueLight (alfabetic)
  Many tnx to those who helped testing:
     Arnau, Bjarni, and tokai (alfabetic)
  And to all other people who helped testing and sending comments / bugs
  Stats: 673 lines changed, 3534 new lines, 79 new strings

engine.c

@@ -30,6 +30,10 @@ enum {
 	ENGINE_PREVIEWING = 4,
 };
 
+enum {
+	YEAR_ENGINE_AGING_STOPS = 2050,
+};
+
 /** Bitmasked values of what type of cargo is refittable for the given vehicle-type.
  * This coupled with the landscape information (_landscape_global_cargo_mask) gives
  * us exactly what is refittable and what is not */
@@ -135,6 +139,8 @@ void StartupEngines(void)
 {
 	Engine *e;
 	const EngineInfo *ei;
+	/* Aging of vehicles stops, so account for that when starting late */
+	const uint16 aging_date = min(_date, ConvertYMDToDate(YEAR_ENGINE_AGING_STOPS, 0, 1));
 
 	SetupEngineNames();
 
@@ -152,7 +158,7 @@ void StartupEngines(void)
 		r = Random();
 		e->intro_date = ei->base_intro <= ConvertYMDToDate(1922, 0, 1) ? ei->base_intro : (Date)GB(r, 0, 9) + ei->base_intro;
 		if (e->intro_date <= _date) {
-			e->age = (_date - e->intro_date) >> 5;
+			e->age = (aging_date - e->intro_date) >> 5;
 			e->player_avail = (byte)-1;
 			e->flags |= ENGINE_AVAILABLE;
 		}
@@ -237,7 +243,7 @@ void EnginesDailyLoop(void)
 {
 	EngineID i;
 
-	if (_cur_year >= 2050) return;
+	if (_cur_year >= YEAR_ENGINE_AGING_STOPS) return;
 
 	for (i = 0; i != lengthof(_engines); i++) {
 		Engine *e = &_engines[i];
@@ -358,7 +364,7 @@ void EnginesMonthlyLoop(void)
 {
 	Engine *e;
 
-	if (_cur_year < 2050) {
+	if (_cur_year < YEAR_ENGINE_AGING_STOPS) {
 		for (e = _engines; e != endof(_engines); e++) {
 			// Age the vehicle
 			if (e->flags & ENGINE_AVAILABLE && e->age != 0xFFFF) {