some improvement to alfd/plane interaction

OpenRA.Mods.RA/Activities/ReturnToBase.cs

@@ -35,10 +35,17 @@ namespace OpenRA.Mods.RA.Activities
 
 		void Calculate(Actor self)
 		{
-			if (dest == null) dest = ChooseAirfield(self);
+			if (dest == null)
+			{
+				dest = ChooseAirfield(self);
 				var res = dest.traits.GetOrDefault<Reservable>();
 				if (res != null)
-				self.traits.Get<Plane>().reservation = res.Reserve(self);
+				{
+					var plane = self.traits.Get<Plane>();
+					plane.UnReserve();
+					plane.reservation = res.Reserve(self);
+				}
+			}
 
 			var landPos = dest.CenterLocation;
 			var aircraft = self.traits.Get<Aircraft>();

OpenRA.Mods.RA/Plane.cs

@@ -74,7 +74,7 @@ namespace OpenRA.Mods.RA
 			return (order.OrderString == "Move" || order.OrderString == "Enter") ? "Move" : null;
 		}
 
-		void UnReserve()
+		public void UnReserve()
 		{
 			if (reservation != null)
 			{
@@ -130,7 +130,10 @@ namespace OpenRA.Mods.RA
 						? (IActivity)new Rearm() : new Repair(order.TargetActor));
 			}
 			else
+			{
+				Game.Debug("Unreserve due to unhandled order: {0}".F(order.OrderString));
 				UnReserve();
 			}
 		}
+	}
 }

OpenRA.Mods.RA/Reservable.cs

@@ -36,6 +36,10 @@ namespace OpenRA.Mods.RA
 
 		public IDisposable Reserve(Actor forActor)
 		{
+			if (reservedFor != null)
+				Game.Debug("BUG: #{0} {1} was already reserved (by #{2} {3})".F(
+					self.ActorID, self.Info.Name, reservedFor.ActorID, reservedFor.Info.Name));
+
 			reservedFor = forActor;
 			Game.Debug("#{0} {1} reserved by #{2} {3}".F(
 				self.ActorID, self.Info.Name, forActor.ActorID, forActor.Info.Name));