def as_graph_queue(self, manifest, limit_to=None):
        """Returns a queue over nodes in the graph that tracks progress of
        dependecies.
        """
        if limit_to is None:
            graph_nodes = self.graph.nodes()
        else:
            graph_nodes = limit_to

        new_graph = _subset_graph(self.graph, graph_nodes)
        return GraphQueue(new_graph, manifest)
Returns a queue over nodes in the graph that tracks progress of
        dependecies.