Revamping/cleanup of how we handle authentication usernames as well as chained

authenticators and chained session factories. We can share a lot more code this
way and the implicit requirement that the default authenticator/factory had to
be configured before anyone else configured a chanied author/factory is gone.

The other big change is that Credentials doesn't require a username
(UsernamePasswordCreds inherits that username so most derived classes don't
notice any difference). Instead we require that a canonical authentication
username be determined and configured in AuthingConnection during the
authentication process. This canonical username is then used to resolve the
client session and map everything in the client manager.

This is pretty much exactly what was going on before except that we were doing
it all in an ad hoc way by jamming a new name into Credentials during the
authentication process and also doing jiggery pokery in
PresentsSession.assignStartingUsername. That all goes away and/or becomes
cleaner and more explicit.

This is going to impact some Yohoho jiggery pokery, which I will shortly commit
a patch for, but we're going to need to test it. Omelets, eggs, etc.


git-svn-id: svn+ssh://src.earth.threerings.net/narya/trunk@5828 542714f4-19e9-0310-aa3c-eee0fc999fb1

etc/libs-incl.xml

@@ -19,5 +19,6 @@
     <include name="swfutils-ooo.jar"/>
     <include name="velocity-1.5-dev.jar"/>
     <include name="thane*.swc"/>
+    <include name="corelib.swc"/>
   </fileset>
 </project>