added --dry_run, removed --mapping_session_id, other fixes
added --dry_run, removed --mapping_session_id, other fixes

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