* autoload.cc (PrivilegeCheck): Define.

	* autoload.cc (PrivilegeCheck): Define.
	* fhandler.cc (fhandler_base::open): Always try opening with backup
	resp. restore intent.
	* fhandler_disk_file.cc (fhandler_disk_file::opendir): Always try
	opening with backup intent.
	(fhandler_disk_file::readdir): Ditto when trying to retrieve file id
	explicitely.
	* security.cc (check_file_access): Replace pbuf with correctly
	PPRIVILEGE_SET typed pset.  Check explicitely for backup and/or restore
	privileges when AccessCheck fails, to circumvent AccessCheck
	shortcoming.  Add comment to explain.