'A connection to server either went down, or was never made.
We distinguish by whether it is in self.interfaces.'

def connection_down(self, server):

    self.disconnected_servers.add(server)
    if (server == self.default_server):
        self.set_status('disconnected')
    if (server in self.interfaces):
        self.close_interface(self.interfaces[server])
        self.notify('interfaces')
    for b in self.blockchains.values():
        if (b.catch_up == server):
            b.catch_up = None
