(svn r1817) -Codechange: Moved depot-functions to depot.c

-Codechange: Added wrappers around depot-access (GetDepot no exists)
-Codechange: Made depot-functions a bit more logic (no longer 
GetDepotByTile crashes your game when you request it on a non-depot tile)
-Add: made depots dynamic (yes, 64k depots are possible now)

depot.h

@@ -0,0 +1,51 @@
+#ifndef DEPOT_H
+#define DEPOT_H
+
+#include "pool.h"
+
+struct Depot {
+	TileIndex xy;
+	uint16 town_index;
+	uint16 index;
+};
+
+extern MemoryPool _depot_pool;
+
+/**
+ * Get the pointer to the depot with index 'index'
+ */
+static inline Depot *GetDepot(uint index)
+{
+	return (Depot*)GetItemFromPool(&_depot_pool, index);
+}
+
+/**
+ * Get the current size of the DepotPool
+ */
+static inline uint16 GetDepotPoolSize(void)
+{
+	return _depot_pool.total_items;
+}
+
+#define FOR_ALL_DEPOTS_FROM(d, start) for (d = GetDepot(start); d != NULL; d = (d->index + 1 < GetDepotPoolSize()) ? GetDepot(d->index + 1) : NULL)
+#define FOR_ALL_DEPOTS(d) FOR_ALL_DEPOTS_FROM(d, 0)
+
+#define MIN_SERVINT_PERCENT  5
+#define MAX_SERVINT_PERCENT 90
+#define MIN_SERVINT_DAYS    30
+#define MAX_SERVINT_DAYS   800
+
+VARDEF TileIndex _last_built_train_depot_tile;
+VARDEF TileIndex _last_built_road_depot_tile;
+VARDEF TileIndex _last_built_aircraft_depot_tile;
+VARDEF TileIndex _last_built_ship_depot_tile;
+
+bool IsTrainDepotTile(TileIndex tile);
+bool IsRoadDepotTile(TileIndex tile);
+Depot *GetDepotByTile(uint tile);
+void InitializeDepot(void);
+Depot *AllocateDepot(void);
+bool IsShipDepotTile(TileIndex tile);
+void DoDeleteDepot(uint tile);
+
+#endif /* DEPOT_H */