Allow retrieval of project state at start of migrations

    def __str__(self):

        return "Graph: %s nodes, %s edges" % (len(self.nodes), sum(len(x) for x in self.dependencies.values()))

    def project_state(self, node):

    def project_state(self, node, at_end=True):

        """

        Given a migration node, returns a complete ProjectState for it.

        If at_end is False, returns the state before the migration has run.

        """

        plan = self.forwards_plan(node)

        if not at_end:

            plan = plan[:-1]

        project_state = ProjectState()

        for node in plan:

            project_state = self.nodes[node].mutate_state(project_state)