With this patch we can use \N in attributes of posting-style, this is
usefull when using several email on a domain, like:

--8<---------------cut here---------------start------------->8---
(setq gnus-posting-styles
      '(("mydomain.\\(.*\\)"
         (name "Daniel Dehennin")
         (address "\\1@mydomain")
         (signature-file "~/.signature.mydomain.\\1"))))
--8<---------------cut here---------------end--------------->8---

This only works for string match on group name.

------------------------------------------------------------
revno: 142
committer: Daniel Dehennin <daniel.dehennin@baby-gnu.org>
branch nick: posting-style
timestamp: Tue 2009-07-07 23:02:32 +0200
message:
  Use replace-match in posting-style.
  
  * lisp/gnus-msg.el (gnus-configure-posting-styles): If the value is a
    string and if the match is a group name (string)
  
  * texi/gnus.texi (Posting Styles): Add documentation on replace-match call.