maintaining.texi: Suopport fo Arch has been moved to obolte.

Remove references that imply otherwise.
Make gnutls-peer-status return even more data

* src/gnutls.c (Fgnutls_peer_status): Return the key exchange, cipher
and MAC algorithms.
* lisp/net/nsm.el (nsm-check-protocol): Test for RC4 on `high'.