OStatus/FeedSub: tweaked PuSH feed garbage collection so other plugins can declare usage of a low-level feed or an OStatus profile besides profile subscriptions & group memberships.

SubMirror: redid add-mirror frontend to accept a feed URL, then pass that on to OStatus, instead of pulling from your subscriptions.
Profile: tweaked subscriberCount() so it doesn't subtract 1 for foreign profiles who aren't subscribed to themselves; instead excludes the self-subscription in the count query.
Memcached_DataObject: tweak to avoid extra error spew in the DB error raising

Work in progress: tweaking feedsub garbage collection so we can count other uses

classes/Memcached_DataObject.php

@@ -574,7 +574,7 @@ class Memcached_DataObject extends Safe_DataObject
     function raiseError($message, $type = null, $behaviour = null)
     {
         $id = get_class($this);
-        if ($this->id) {
+        if (!empty($this->id)) {
             $id .= ':' . $this->id;
         }
         if ($message instanceof PEAR_Error) {