Some sources (e.g. TIGR Gene Index) reuse accessions between species. I have...

Some sources (e.g. TIGR Gene Index) reuse accessions between species. I have therefore altered the "insert_or_select" and "get_xref_id_by_accession_and_source" functions so that they accept a species arg. The UNIQUE key on the xref table has also been updated with the addition of the species field