Log threshold and environment

I think it could be useful to have the environment affect what is logged through log_message(). It is currently possible to limit logs by editing $config['log_threshold'] in config.php, but it's kind of annoying to have to edit your config files every time you move to your production or testing environment.

Why not make the environment constant drive what is logged and what is not? The config file could even specify a log threshold for each environment.