Added termcombination field in triple tables (used to facilitate term roundtripping - can be used as an additional index).  Added REGEXTerm support.  Completed contexts method (with triples)
Added termcombination field in triple tables (used to facilitate term roundtripping - can be used as an
additional index).  Added REGEXTerm support.  Completed contexts method (with triples)

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