'Switch to server as our interface.  If no connection exists nor
being opened, start a thread to connect.  The actual switch will
happen on receipt of the connection notification.  Do nothing
if server already is our interface.'

def switch_to_interface(self, server):

    self.default_server = server
    if (server not in self.interfaces):
        self.interface = None
        self.start_interface(server)
        return
    i = self.interfaces[server]
    if (self.interface != i):
        self.print_error('switching    to', server)
        self.interface = i
        self.send_subscriptions()
        self.set_status('connected')
        self.notify('updated')
