'Unregister a handler instance by name with esc_strings.'

def unregister_handler(self, name, handler, esc_strings):

    try:
        del self._handlers[name]
    except KeyError:
        pass
    for esc_str in esc_strings:
        h = self._esc_handlers.get(esc_str)
        if (h is handler):
            del self._esc_handlers[esc_str]
