dirname() is a slow function compared with __DIR__ and using
'/../'. Moodle has a large number of legacy files that are included
each time a page loads and is not able to use an autoloader as it is
functional code. This allows those required includes to perform as
best as possible in this situation.
A stand-in for sendmail that will log all emails instead of sending
them out. Use when debugging cron performance and output.
References:
MDL-12142
http://moodle.org/mod/forum/post.php?reply=349457