test for #494 (canonicalization sometimes collapses BNodes)
test for #494 (canonicalization sometimes collapses BNodes)

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