Several places in admin/mnet pull in required files using a hardcoded
admin dir string, as this is configurable it needs to use $CFG->admin
instead.
Places where the url is passed through moodle_url don't need to be
updated as that already automatically translates the urls for us.
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.
Adam Olley