Partly revert 97830b0701 (thanks _MrB_)

require_once lines were required since _plugins_ don't __autoload

Also, Realtime would load the wrong URL for css/js since $this->name()
returns get_class($this) instead of the calling class' __CLASS__.

plugins/Comet/CometPlugin.php

@@ -31,6 +31,8 @@ if (!defined('GNUSOCIAL') && !defined('STATUSNET')) {
     exit(1);
 }
 
+require_once INSTALLDIR.'/plugins/Realtime/RealtimePlugin.php';
+
 /**
  * Plugin to do realtime updates using Comet
  *