mod_dialback: never attempt to do dialback on unencrypted streams if tls is mandated.
(Fixes #72)
mod_{dialback/s2s}: do some refactoring of previous commits...
- If s2s encryption is required drop down namespace declaration of dialback on the
stream header and make it completely compliant with RFC 6120
- Fix a traceback in mod_dialback
mod_s2s: close down streams to pre-1.0 servers if stream enc. is required. (Fixes #73)
mod_s2s: deal a bit more coherently with :close() in this case.
util.xmppstream: fix a traceback, related to previous commits.