Autolinking of glossaries, activity, resources and wiki names were using a
trivial single-entry cache implemented with static vars. The cache was _not_
keyed on course.
This bug was visible during forum_cron() which walks many courses. The cache
would get "stuck" on the first course that had something to put in the cache.
All mailouts from there onwards would autolink to stuff in the wrong course.
with Turck MMCache.
Filter function must now have a particular name
eg resource_filter
where "resource" is the name of the directory that filter.php is in.
I've left out stuff that didn't seem necessary ... including a lot
of the Wiki plugins which were quote large... I'm not sure if this
is currently working ... I'm about to try it out.