Patch for SASL External authentication

[Jajcus]

Hi,

I'm working on jabberd2 to implement c2s SASL external authentication based on TLS certificates.

I've used pyxmpp as the testing library for the connections and I can only say it works :)

Implemented stuff:

1. Fixed deprecated m2crypto client certificate stuff
2. Added SASL external authenticator
3. Modified bits of code to make it work.

The following stadards were used:

1. RFC3920bis (http://mail.jabber.org/pipermail/standards/2008-June/018939.html)
2. XEP-0178 (http://xmpp.org/extensions/xep-0178.html#c2s)

The following patch is made against pyxmpp-1.0.1 release tarball. I'm also attaching a testing script which successfully connects to my modified jabberd2 server (patches to that server will be posted soon).

[Jajcus]

Duplicate of #35.

--jajcus