daemon,greeter: login after PAM has had time to talk to user
    
    The greeter currently gives the go ahead for the session to start
    as soon as the user has been authorized.  Then the slave quickly
    runs through the remaining hoops and the greeter gets promptly
    killed.
    
    This commit changes the logic so that the slave doesn't get the
    go ahead to start the session until all the hoops have been
    run through, and potential messages have been queued, and displayed.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=583856