Stomp queue restructuring for mass scalability:

- Multiplexing queues into groups and for multiple sites.
- Sharing vs breakout configurable per site and per queue via $config['queue']['breakout']
- Detect how many times a message is redelivered, discard if it's killed too many daemons
 - count configurable with $config['queue']['max_retries']
 - can dump the items to files in $config['queue']['dead_letter_dir']

Queue daemon memory & resource leak fixes:
- avoid unnecessary reconnections to memcached server (switch persistent connections back in on second initialization, assuming it's child process)
- monkey-patch for leaky .ini loads in DB_DataObject::databaseStructure() - was leaking 200k per active switch
- applied leak fixes to Status_network as well, using intermediate base Safe_DataObject for both it and Memcache_DataObject

Misc queue fixes:
- correct handling of child processes exiting due to signal termination instead of regular exit
- shutdown instead of infinite respawn loop if we're already past the soft memory limit at startup
- Added --all option for xmppdaemon... still opens one xmpp connection per site that has xmpp active

Cache updates:
- add Cache::increment() method with native support for memcached atomic increment

lib/statusnet.php

@@ -101,6 +101,60 @@ class StatusNet
         self::initPlugins();
     }
 
+    /**
+     * Get identifier of the currently active site configuration
+     * @return string
+     */
+    public static function currentSite()
+    {
+        return common_config('site', 'nickname');
+    }
+
+    /**
+     * Change site configuration to site specified by nickname,
+     * if set up via Status_network. If not, sites other than
+     * the current will fail horribly.
+     *
+     * May throw exception or trigger a fatal error if the given
+     * site is missing or configured incorrectly.
+     *
+     * @param string $nickname
+     */
+    public static function switchSite($nickname)
+    {
+        if ($nickname == StatusNet::currentSite()) {
+            return true;
+        }
+
+        $sn = Status_network::staticGet($nickname);
+        if (empty($sn)) {
+            return false;
+            throw new Exception("No such site nickname '$nickname'");
+        }
+
+        $server = $sn->getServerName();
+        StatusNet::init($server);
+    }
+
+    /**
+     * Pull all local sites from status_network table.
+     *
+     * Behavior undefined if site is not configured via Status_network.
+     *
+     * @return array of nicknames
+     */
+    public static function findAllSites()
+    {
+        $sites = array();
+        $sn = new Status_network();
+        $sn->find();
+        while ($sn->fetch()) {
+            $sites[] = $sn->nickname;
+        }
+        return $sites;
+    }
+
+
     /**
      * Fire initialization events for all instantiated plugins.
      */