namespaces: add nodemap property This patch adds a node-to-name map property to the namespace. This is necessary because we cannot simply invert the name-to-node map because we do not assume the name-to-node map to be unique (for example, consider named branches: many nodes have one branch name). The node-to-name is helpful in log commands where we are already iterating over a set of nodes and want to display some kind of naming information to the user.