WP_Importer::set_user( int $user_id )

	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;
	}