fixes to GRAPH evaluation and 'hooks'/checks for compliance with formal SPARQL datasets (default graphs in particular).
fixes to GRAPH evaluation and 'hooks'/checks for compliance with formal SPARQL datasets (default graphs in particular).

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