WP_Importer::set_user

	public function set_user( $user_id ) {
		if ( is_numeric( $user_id ) ) {
			$user_id = (int) $user_id;
		} else {
			$user_id = (int) username_exists( $user_id );
		}

		if ( ! $user_id || ! wp_set_current_user( $user_id ) ) {
			fwrite( STDERR, "Error: can not find user\n" );
			exit;
		}

		return $user_id;
	}