Add set_consume which always takes ownership

Freeing in error path is the common pattern with set_put().

src/core/dbus-manager.c

@@ -1186,11 +1186,9 @@ static DBusHandlerResult bus_manager_message_handler(DBusConnection *connection,
                 if (!client)
                         goto oom;
 
-                r = set_put(s, client);
-                if (r < 0) {
-                        free(client);
+                r = set_consume(s, client);
+                if (r < 0)
                         return bus_send_error_reply(connection, message, NULL, r);
-                }
 
                 reply = dbus_message_new_method_return(message);
                 if (!reply)

src/core/load-fragment.c

@@ -2095,11 +2095,9 @@ static int open_follow(char **filename, FILE **_f, Set *names, char **_final) {
                                 if (!id)
                                         return -ENOMEM;
 
-                                r = set_put(names, id);
-                                if (r < 0) {
-                                        free(id);
+                                r = set_consume(names, id);
+                                if (r < 0)
                                         return r;
-                                }
                         }
                 }
 

src/core/manager.c

@@ -806,11 +806,9 @@ static void manager_build_unit_path_cache(Manager *m) {
                                 goto fail;
                         }
 
-                        r = set_put(m->unit_path_cache, p);
-                        if (r < 0) {
-                                free(p);
+                        r = set_consume(m->unit_path_cache, p);
+                        if (r < 0)
                                 goto fail;
-                        }
                 }
 
                 closedir(d);

src/core/mount-setup.c

@@ -251,10 +251,9 @@ int mount_cgroup_controllers(char ***join_controllers) {
                         continue;
                 }
 
-                r = set_put(controllers, controller);
+                r = set_consume(controllers, controller);
                 if (r < 0) {
                         log_error("Failed to add controller to set.");
-                        free(controller);
                         goto finish;
                 }
         }