delete last town is just the inverse of create town

src/tools/undo.cpp

@@ -23,13 +23,13 @@ cAction::~cAction() {}
 
 void cAction::undo() {
 	UNDO_LOG("Undoing " + actname);
-	if(done && undo_me())
+	if(done && reversed ? redo_me() : undo_me())
 		done = false;
 }
 
 void cAction::redo() {
 	UNDO_LOG("Redoing " + actname);
-	if(!done && redo_me())
+	if(!done && reversed ? undo_me() : redo_me())
 		done = true;
 }
 

src/tools/undo.hpp

@@ -23,7 +23,9 @@ class cAction {
 protected:
 	/// Construct a named action
 	/// @param name The name of the action to show in the Edit menu
-	cAction(std::string name) : actname(name) {}
+	cAction(std::string name, bool reversed = false) : actname(name), reversed(reversed) {}
+	/// For actions that have an inverse, this flag inverts the action implementation (i.e. create/delete)
+	bool reversed = true;
 public:
 	/// Undoes this action if it has not already been undone.
 	/// If it has already been undone, does nothing.