added formula_aware attribute, support for Variable roundtriping and removed references to SubGraph
added formula_aware attribute, support for Variable roundtriping and removed references to SubGraph


git-svn-id: 60eb48102d1ca0c284ab3654bef916b01e1b221b@464 4f84a9ca-5c3e-0410-8a68-0bdf370325d5

nwebs/rdflib