added argument checking to get_mapping_path
added argument checking to get_mapping_path

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