Add current order (station, waypoint or depot) condition variable.

Adjust item bit allocations:
* Increase cond flags from 2 bits to 3 bits, for future expansion.
* Use 2 bits remaining in adjacent gap for an auxiliary type field.
  This is used for the type (station, waypoint, etc.) of order tests.
Perform a linear scan of the program pool when deleting a station,
waypoint or depot.

src/depot.cpp

@@ -17,6 +17,7 @@
 #include "core/pool_func.hpp"
 #include "vehicle_gui.h"
 #include "vehiclelist.h"
+#include "tracerestrict.h"
 
 #include "safeguards.h"
 
@@ -42,6 +43,8 @@ Depot::~Depot()
 	/* Clear the depot from all order-lists */
 	RemoveOrderFromAllVehicles(OT_GOTO_DEPOT, this->index);
 
+	TraceRestrictRemoveDestinationID(TROCAF_DEPOT, this->index);
+
 	/* Delete the depot-window */
 	DeleteWindowById(WC_VEHICLE_DEPOT, this->xy);