Client: Moved Authentication handling at the RequestHandler level.
Client: Completed the proposed authentication model and existing tests.
Client: plugged the new RegistrationTask in UserAgent.
Client: added preliminary and quite empty dialog objects.
Merge branch 'master' into ds-client-calls
Client: plugged UserAgent, Call and SessionHandler altogether.
Merge branch 'master' into ds-client-reg-auth
Cipango-client: Call
Client: wrote ChallengedMessageHandler out of MessageHandler.
Client: revamped Registration to accept more than one listener.

This simplifies the implementation of RegistrationTask.
Client: Introduced the AuthenticationHelper.

Also now RequestHandler and SessionHandler both inherit the brand new
DefaultChallengedMessageHandler, which contains the bare
behaviour for such handlers. 
Add outboud proxy
Client: Renamed AbstractDialog into Dialog - with other small tweaks and
typo fixes.
Client: Added handlers for initial requests on the UserAgent.

The UserAgent can now be associated to a MessageHandler instance to take
care of initial requests. If no handler is set, a DefaultMessageHandler
is used (which refuses everything). The AsyncMessageHandler can provide
asynchronous notifications to listeners.
Merge branch 'ds-client-calls' into ds-client-integration

Conflicts:
	cipango-client/src/main/java/org/cipango/client/SipClient.java
Client: plugged authentication in SessionHandler.
Allow IPv6 address in SIP URI
Client: Fixed SessionHandler members initialization.
Client: Fixed spurious logging in ClientServlet.doRequest.
Client: Fixed AuthenticationHelper.