Do not fall back to using nobody if _user is missing, but

error out.
Add a new user _rwalld for rpc.rwalld, and use that instead
of nobody, also unconditionally drop to _rwalld not only
if rpc.rwalld was started with euid 0 (as root).
ok deraadt@

src/etc/master.passwd

@@ -42,4 +42,5 @@ _rtadvd:*:92:92::0:0:IPv6 Router Advertisement Daemon:/var/empty:/sbin/nologin
 _ypldap:*:93:93::0:0:YP to LDAP Daemon:/var/empty:/sbin/nologin
 _btd:*:94:94::0:0:Bluetooth Daemon:/var/empty:/sbin/nologin
 _smtpd:*:95:95::0:0:SMTP Daemon:/var/empty:/sbin/nologin
+_rwalld:*:96:96::0:0:rpc.rwalld:/var/empty:/sbin/nologin
 nobody:*:32767:32767::0:0:Unprivileged user for NFS:/nonexistent:/sbin/nologin