getUser calls are much more strict, and one place where this was found was
in the (un)subscribe start/end event handlers, which resulted in making the
Subscription class a bit stricter, regarding ::start and ::cancel at least.
Several minor fixes in many files were made due to this.
This does NOT touch the Foreign_link function, which should also have a more
strict getUser call. That is a future project.
lib/plugin.php now has a parent onAutoload function that finds most common
files that are used in plugins (actions, dataobjects, forms, libs etc.) if
they are put in the standardised directories ('actions', 'classes', 'forms',
'lib' and perhaps some others in the future).
