Only join with seq_region and coord_system in generic_fetch() if this is a multi-species database.
Only join with seq_region and coord_system in generic_fetch() if this is
a multi-species database.

API passes unit tests.

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