Passing parameters to implode() in reverse order is deprecated, use
implode($glue, $parts) instead of implode($parts, $glue).
This commit corresponds to phpunit and manual detections, core files.
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.
