added fetch_by_db_accession method
added fetch_by_db_accession method

muffato/ensembl,james-monkeyshines/ensembl,Ensembl/ensembl,Ensembl/ensembl,mjg17/ensembl,at7/ensembl,willmclaren/ensembl,at7/ensembl,muffato/ensembl,Ensembl/ensembl,mjg17/ensembl,danstaines/ensembl,willmclaren/ensembl,muffato/ensembl,james-monkeyshines/ensembl,mjg17/ensembl,Ensembl/ensembl,muffato/ensembl,danstaines/ensembl,james-monkeyshines/ensembl,danstaines/ensembl,at7/ensembl,at7/ensembl,james-monkeyshines/ensembl,mjg17/ensembl