Initial support for ping service

It makes sense to use the weblogs.com ping service to alert people to
changes on the site. So, we do. Includes an extra ping queue handler.

lib/common.php

@@ -128,6 +128,8 @@ $config =
         array('enabled' => false,
               'server' => 'localhost',
               'port' => 11211),
+ 		'ping' =>
+        array('notify' => array()),
         'inboxes' =>
         array('enabled' => true), # on by default for new sites
         );