added default for prefix declarations (to accomodate change in grammar)
added default for prefix declarations (to accomodate change in grammar)

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