Provide more accurate exception reporting for missing bsddb/bsddb3.
Provide more accurate exception reporting for missing bsddb/bsddb3.

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