closes #2874: improved ingame chat

OpenRA.Game/Network/Session.cs

@@ -59,6 +59,7 @@ namespace OpenRA.Network
 			public string Bot; // Bot type, null for real clients
 			public bool IsAdmin;
 			public bool IsReady { get { return State == ClientState.Ready; } }
+			public bool IsObeserver { get { return Slot == null; } }
 		}
 
 		public class Slot

OpenRA.Game/Network/UnitOrders.cs

@@ -44,6 +44,7 @@ namespace OpenRA.Network
 						{
 							var player = world != null ? world.FindPlayerByClient(client) : null;
 							var suffix = (player != null && player.WinState == WinState.Lost) ? " (Dead)" : "";
+							suffix = client.IsObeserver ? " (Spectator)" : suffix;
 							Game.AddChatLine(client.ColorRamp.GetColor(0), client.Name + suffix, order.TargetString);
 						}
 						else