First steps on converting FeedSub into the pub/sub basis for OStatus communications:

* renamed FeedSub plugin to OStatus
* now setting avatar on subscriptions
* general fixes for subscription
* integrated PuSH hub to handle only user timelines on canonical ID url; sends updates directly
* set $config['feedsub']['nohub'] = true to test w/ foreign feeds that don't have hubs (won't actually receive updates though)
* a few bits of code documentation
* HMAC support for verified distributions (safest if sub setup is on HTTPS)

And a couple core changes:
* minimizing HTML output for exceptions in API requests to aid in debugging
* fix for rel=self link in apitimelineuser when id given

This does not not yet include any of the individual subscription management (Salmon notifications for sub/unsub, etc) nor a nice UI for user subscriptions.
Needs some further cleanup to treat posts as status updates instead of link references.

lib/error.php

@@ -56,6 +56,7 @@ class ErrorAction extends Action
 
         $this->code = $code;
         $this->message = $message;
+        $this->minimal = StatusNet::isApi();
 
         // XXX: hack alert: usually we aren't going to
         // call this page directly, but because it's
@@ -102,7 +103,14 @@ class ErrorAction extends Action
 
     function showPage()
     {
-        parent::showPage();
+        if ($this->minimal) {
+            // Even more minimal -- we're in a machine API
+            // and don't want to flood the output.
+            $this->extraHeaders();
+            $this->showContent();
+        } else {
+            parent::showPage();
+        }
 
         // We don't want to have any more output after this
         exit();