Fix bugs in invite/join dances.

We now do more implement more of the auth on the events so that we
don't reject valid events.

synapse/handlers/_base.py

@@ -78,7 +78,7 @@ class BaseHandler(object):
 
         if not suppress_auth:
             logger.debug("Authing...")
-            self.auth.check(event, raises=True)
+            self.auth.check(event, auth_events=event.old_state_events)
             logger.debug("Authed")
         else:
             logger.debug("Suppressed auth.")