Optional reconnect functionality

Enable the server to request the client to reconnect.

This can be done with the now extended minetest.request_shutdown([reason], [reconnect]) setting.

src/game.h

@@ -147,6 +147,7 @@ void the_game(bool *kill,
 		u16 port,
 		std::string &error_message,
 		ChatBackend &chat_backend,
+		bool *reconnect_requested,
 		const SubgameSpec &gamespec, // Used for local game
 		bool simple_singleplayer_mode);