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.
For pages where there will be significant user interaction in which the
server is not updated, it may be necessary to poll the server periodically
to touch the session.
This makes use of the existing checknet script which was designed for
checking network connectivity but fits into this use-case reasonably well.