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/actions/pushcallback.php

@@ -29,6 +29,7 @@ class PushCallbackAction extends Action
 {
     function handle()
     {
+        StatusNet::setApi(true); // Minimize error messages to aid in debugging
         parent::handle();
         if ($_SERVER['REQUEST_METHOD'] == 'POST') {
             $this->handlePost();