If your Catalyst project logs many messages, logging via standard error to
Apache's error log is not very clean: The log messages are mixed with
other web applications' noise; and especially if you use mod_fastcgi,
every line will be prepended with a long prefix.

An alternative is logging to a file. But then you have to make sure that
multiple processes won't corrupt the log file. The module Log::Handler
by Jonny Schulz does exactly this, because it supports message-wise flocking.

This module is a wrapper for said Log::Handler.
