added equivalences to rdfv3 for datasets with get_xrefs method
added get_xrefs to entrez and swissprot datasets
moved affy array names from parsers to configuration
updated equiv to use get_xrefs
added command line option to rdfv3 to limit rdf output to specified dataset
added get_xref method for affy dataset
fixed problems with equiv
integrated get_xref method for affy into equiv.py
renamed rdfv3.py to rdf.py