Modification to retrieval by synonym to cope with orphan marker_synonym->marker links in mouse. fetch_by_dbID only warns (rather than throwing) if the dbID does not exist, and fetch_all_by_synonym only returns valid markers.
Modification to retrieval by synonym to cope with orphan marker_synonym->marker links in mouse.
fetch_by_dbID only warns (rather than throwing) if the dbID does not exist, and fetch_all_by_synonym only returns valid markers.

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