(svn r2669) Shuffle some more stuff around to reduce dependencies

airport.c

@@ -3,6 +3,8 @@
 #include "debug.h"
 #include "map.h"
 #include "airport.h"
+#include "macros.h"
+#include "variables.h"
 
 AirportFTAClass *CountryAirport;
 AirportFTAClass *CityAirport;
@@ -359,3 +361,14 @@ const AirportFTAClass* GetAirport(const byte airport_type)
 	}
 	return Airport;
 }
+
+uint32 GetValidAirports(void)
+{
+	uint32 bytemask = _avail_aircraft; /// sets the first 3 bytes, 0 - 2, @see AdjustAvailAircraft()
+
+	// 1980-1-1 is --> 21915
+	// 1990-1-1 is --> 25568
+	if (_date >= 21915) {SETBIT(bytemask, 3);}	// metropilitan airport 1980
+	if (_date >= 25568) {SETBIT(bytemask, 4);}	// international airport 1990
+	return bytemask;
+}