Install (optional) libutil.h with prototypes for the functions and
document this in the man page.
minor cleanups to the various routines, include the prototype file, declare
return codes etc.
replace the dozen other various hacks in the code that do all sorts
of crude things including spamming the envrionment strings with the new
argv string.
This version is mainly inspired by the sendmail version, with a couple of
ideas taken from the NetBSD implementation as well.
'NIS information unchanged' or '/etc/master.passwd unchanged'
depending on which was is being modified (conditional on -DYP).
This is to save me the trouble of writing a whole other error
routine (nis_error()?) for the upcoming changes to passwd and
chpass.
