fixed typo; added DeprecationWarning for when BackwardCompatGraph is used
fixed typo; added DeprecationWarning for when BackwardCompatGraph is used

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