OStatus PuSH fixlets:

- set minimal error page output on PuSH callback
- allow hub to retry ($config['ostatus']['hub_retries']), simplify internal iface a bit. Retries are pushed to end of queue but otherwise not delayed yet; makes delivery more robust to one-off transitory errors but not yet against downtime.

plugins/OStatus/lib/hubdistribqueuehandler.php

@@ -124,10 +124,7 @@ class HubDistribQueueHandler extends QueueHandler
         common_log(LOG_INFO, "Preparing $sub->N PuSH distribution(s) for $sub->topic");
         $qm = QueueManager::get();
         while ($sub->fetch()) {
-            common_log(LOG_INFO, "Prepping PuSH distribution to $sub->callback for $sub->topic");
-            $data = array('sub' => clone($sub),
-                          'atom' => $atom);
-            $qm->enqueue($data, 'hubout');
+            $sub->distribute($atom);
         }
     }