Make _objs_from_sth() aware of circular chromosomes.  Patch from EG.
Make _objs_from_sth() aware of circular chromosomes.  Patch from EG.

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