dovecot: create dovenull user/group (see note)

Note:

Starting with version 2.0 dovecot needs an dedicated user/group for
unprivileged login processes called 'dovenull'.

mail/dovecot/postsysfiles.in

@@ -2,7 +2,7 @@
 # This copyright note is auto-generated by ./scripts/Create-CopyPatch.
 #
 # Filename: package/.../dovecot/postsysfiles.in
-# Copyright (C) 2007 The OpenSDE Project
+# Copyright (C) 2007 - 2011 The OpenSDE Project
 #
 # More information can be found in the files COPYING and README.
 #
@@ -13,6 +13,8 @@
 # --- SDE-COPYRIGHT-NOTE-END ---
 
 safe_groupadd dovecot 97
+safe_groupadd dovenull 98
 
 safe_useradd dovecot 97 97 "Dovecot IMAP/POP3 daemon" /var/empty /bin/false "*"
+safe_useradd dovenull 98 98 "Dovecot IMAP/POP3 login" /var/empty /bin/false "*"