add proper entries for pkg_add privsep, instead of piggy-backing on _pfetch

which was a "better than nothing" measure for 5.9.
Another user to come. Approved by deraadt@ on principle.
thanks sthen@ for checking my lines over.

src/etc/group

@@ -26,6 +26,8 @@ _unbound:*:53:
 _dpb:*:54:
 _pbuild:*:55:
 _pfetch:*:56:
+_pkgfetch:*:57:
+_pkguntar:*:58:
 _spamd:*:62:
 _radius:*:63:
 _token:*:64:

src/etc/mail/aliases

@@ -1,5 +1,5 @@
 #
-#	$OpenBSD: aliases,v 1.55 2015/12/16 18:19:25 ratchov Exp $
+#	$OpenBSD: aliases,v 1.56 2016/03/05 12:31:38 espie Exp $
 #
 #  Aliases in this file will NOT be expanded in the header from
 #  Mail, but WILL be visible over networks or from /usr/libexec/mail.local.
@@ -44,6 +44,8 @@ _ospf6d: /dev/null
 _pbuild: /dev/null
 _pfetch: /dev/null
 _pflogd: /dev/null
+_pkgfetch: /dev/null
+_pkguntar: /dev/null
 _portmap: /dev/null
 _ppp: /dev/null
 _radiusd: /dev/null

src/etc/master.passwd

@@ -14,6 +14,8 @@ _unbound:*:53:53:unbound:0:0:Unbound Daemon:/var/unbound:/sbin/nologin
 _dpb:*:54:54::0:0:dpb privsep:/var/empty:/sbin/nologin
 _pbuild:*:55:55:pbuild:0:0:dpb build user:/nonexistent:/sbin/nologin
 _pfetch:*:56:56::0:0:dpb fetch user:/nonexistent:/sbin/nologin
+_pkgfetch:*:57:57::0:0:pkg fetch user:/nonexistent:/sbin/nologin
+_pkguntar:*:58:58::0:0:pkg untar user:/nonexistent:/sbin/nologin
 _spamd:*:62:62::0:0:Spam Daemon:/var/empty:/sbin/nologin
 uucp:*:66:1::0:0:UNIX-to-UNIX Copy:/var/spool/uucppublic:/sbin/nologin
 www:*:67:67::0:0:HTTP Server:/var/www:/sbin/nologin