my network because setnetgrent() was trying to do a lookup on group "".
It seems that an attempt to do a yp_match() (and possible yp_next())
on a null or empty key causes Sun's ypserv in SunOS 4.1.3 to exit
suddenly (and without warning). Our ypserv behaves badly in this
situation too, thoush it doesn't appear to crash. In any event, getpwent,
getnetgrent and yp_match() and yp_next() are now extra careful not to
accidentally pass on null or empty arguments.
Also made a small change to getpwent.c to allow +::::::::: wildcarding,
which I had disabled previously.
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