Mod version validation

- Game.CurrentMods property to query the current mods when no orderManager accessible
- Server sends mod versions to master server on ping
- Client sends mod versions on handshake response
- Validate match on server side of handshake, not client side

OpenRA.Game/Server/Server.cs

@@ -188,8 +188,24 @@ namespace OpenRA.Server
 					DropClient(newConn);
 					return;
 				}
-
-				var client = HandshakeResponse.Deserialize(data).Client;
+				
+				var handshake = HandshakeResponse.Deserialize(data);
+				var client = handshake.Client;
+				var mods = handshake.Mods;
+				
+				// Check that the client has compatable mods
+				
+				var valid = mods.All( m => m.Contains('@')) && //valid format
+				            mods.Count() == Game.CurrentMods.Count() &&  //same number
+				            mods.Select( m => Pair.New(m.Split('@')[0], m.Split('@')[1])).All(kv => Game.CurrentMods.ContainsKey(kv.First) &&
+				     		(kv.Second == "{DEV_VERSION}" || Game.CurrentMods[kv.First].Version == "{DEV_VERSION}" || kv.Second == Game.CurrentMods[kv.First].Version));
+				if (!valid) 
+				{
+					Log.Write("server", "Rejected connection from {0}; mods do not match.", 
+						newConn.socket.RemoteEndPoint);
+					DropClient(newConn);
+					return;
+				}
 				
 				// Promote connection to a valid client
 				preConns.Remove(newConn);