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/activityobject.php

@@ -506,7 +506,7 @@ class ActivityObject
 
             $object->poco = PoCo::fromProfile($profile);
 
-            if ($profile->getUser()) {
+            if ($profile->isLocal()) {
                 $object->extra[] = array('followers', array('url' => common_local_url('subscribers', array('nickname' => $profile->nickname))));
             }