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.
Preferences pages cancel and continue buttons should lead back to preferences page.
Site pages should have consistent headers and breadcrumbs.
Hide the "Preferences" node in the navigation.
Part of MDL-45774
