private function __construct( $caller ) {
self::$caller = $caller;
self::$plugins = self::get_options();
add_action( 'admin_init', array( &$this, 'init' ), 100 );
add_filter( 'site_transient_update_plugins', array( &$this, 'update_plugins_filter' ), 1 );
add_action( 'wp_update_plugins', array( &$this, 'check_periodic_updates' ), 99 );
add_action( 'updatecenterplugin_check', array( &$this, 'check_periodic_updates' ) );
add_filter( 'upgrader_post_install', array( &$this, 'upgrader_post_install' ), 99, 3 );
add_filter( 'http_request_args', array( &$this, 'http_request_args' ), 100, 2 );
}