Keep track of removed map elements

Source/Core/Map/Linedef.cs

@@ -153,6 +153,9 @@ namespace CodeImp.DoomBuilder.Map
 				// Already set isdisposed so that changes can be prohibited
 				isdisposed = true;
 
+				if (map == General.Map.Map && General.Network != null && General.Network.ActionRunning)
+					General.Map.Map.RemovedElements.Add(this);
+
 				// Dispose sidedefs
 				if((front != null) && map.AutoRemove) front.Dispose(); else AttachFrontP(null);
 				if((back != null) && map.AutoRemove) back.Dispose(); else AttachBackP(null);

Source/Core/Map/MapSet.cs

@@ -163,6 +163,13 @@ namespace CodeImp.DoomBuilder.Map
 
 		internal bool AutoRemove { get { return autoremove; } set { autoremove = value; } }
 
+		public bool GeometryChanged { set; get; }
+
+		public bool PopulationChanged { set; get; }
+
+		/// <summary>List of all elements that were removed while the previous network action was running</summary>
+		public List<MapElement> RemovedElements { set; get; } = new List<MapElement>();
+
 		#endregion
 
 		#region ================== Constructor / Disposer

Source/Core/Map/Sector.cs

@@ -175,6 +175,9 @@ namespace CodeImp.DoomBuilder.Map
 				// Already set isdisposed so that changes can be prohibited
 				isdisposed = true;
 				
+				if (map == General.Map.Map && General.Network != null && General.Network.ActionRunning)
+					General.Map.Map.RemovedElements.Add(this);
+
 				// Dispose the sidedefs that are attached to this sector
 				// because a sidedef cannot exist without reference to its sector.
 				if(map.AutoRemove)

Source/Core/Map/Sidedef.cs

@@ -127,6 +127,9 @@ namespace CodeImp.DoomBuilder.Map
 				// Already set isdisposed so that changes can be prohibited
 				isdisposed = true;
 
+				if (map == General.Map.Map && General.Network != null && General.Network.ActionRunning)
+					General.Map.Map.RemovedElements.Add(this);
+
 				if(map == General.Map.Map)
 					General.Map.UndoRedo.RecRemSidedef(this);
 

Source/Core/Map/Thing.cs

@@ -162,6 +162,9 @@ namespace CodeImp.DoomBuilder.Map
 			// Not already disposed?
 			if(!isdisposed)
 			{
+				if (map == General.Map.Map && General.Network != null && General.Network.ActionRunning)
+					General.Map.Map.RemovedElements.Add(this);
+
 				if(map == General.Map.Map)
 					General.Map.UndoRedo.RecRemThing(this);
 

Source/Core/Map/Vertex.cs

@@ -118,6 +118,9 @@ namespace CodeImp.DoomBuilder.Map
 				// Already set isdisposed so that changes can be prohibited
 				isdisposed = true;
 
+				if (map == General.Map.Map && General.Network != null && General.Network.ActionRunning)
+					General.Map.Map.RemovedElements.Add(this);
+
 				if(map.AutoRemove)
 				{
 					// Dispose the lines that are attached to this vertex