If a user wishes to change a password on a system running YP, and
the master server is not running rpc.yppasswdd, chpass(1) would fail,
even if the user had a local entry. Fix this by checking for local
entry if master is not running rpc.yppasswd iff we defaulted to using
YP (not invoked with "-y").
XXX Unlike the similar change to passwd(1), this one duplicates some
XXX code (makes an attempt to contact rpc.yppasswdd early). This is
XXX a side-effect of the structure of this program. chpass(1) could
XXX use a re-write.