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.
With the implementation of per-discussion subscription, the current
discussion's subscription state must be shown.
Since this state belongs to the discussion rather than the forum, it
should be shown accordingly. This change therefore includes the addition
of the discussion name as a heading on the page.
