Fix weird dialog shown during login from GDM
    
    When the session manager enters the query end session phase, it
    temporarily adds all clients to the "query clients" list. This list is used to track
    the progression of clients quitting. If a client quits during the query end
    session phase instead of waiting until the end session phase, then it will get
    destroyed but not get removed from the query clients list. This commit
    removes it from the query clients list in this case. It does this by explicitly
    invoking the end session response handler (in effect, the client
    responded to the end session query by exiting).
    
    This prevents a bizarre bug people are seeing where they have to click
    "log out" in a dialog during the login process.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=634244