source has been exhausted. this allows getgrent() across multiple
sources (e.g, ``group: files nis'') to work correctly. the flags are
reset in setgrent()/endgrent().
(as per similar change in getpwent.c rev 1.42)
XXX: this change means that code that uses getgrent() to obtain a list
of groups will have to do duplicate suppression... getgrouplist()
springs to mind; i'm about to modify that
326483c4de