added support for tunneling though a context
added support for tunneling though a context

marma/rdflib,avorio/rdflib,avorio/rdflib,yingerj/rdflib,armandobs14/rdflib,yingerj/rdflib,armandobs14/rdflib,armandobs14/rdflib,ssssam/rdflib,avorio/rdflib,marma/rdflib,marma/rdflib,RDFLib/rdflib,dbs/rdflib,RDFLib/rdflib,yingerj/rdflib,ssssam/rdflib,dbs/rdflib,RDFLib/rdflib,dbs/rdflib,ssssam/rdflib,marma/rdflib,ssssam/rdflib,armandobs14/rdflib,yingerj/rdflib,dbs/rdflib,avorio/rdflib,RDFLib/rdflib