Tidying up getUser calls to profiles and some events

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/apiaction.php

@@ -202,7 +202,11 @@ class ApiAction extends Action
     {
         $twitter_user = array();
 
-        $user = $profile->getUser();
+        try {
+            $user = $profile->getUser();
+        } catch (NoSuchUserException $e) {
+            $user = null;
+        }
 
         $twitter_user['id'] = intval($profile->id);
         $twitter_user['name'] = $profile->getBestName();