Fixes human_status when status is None.  Closes celery/celery#2093
Fixes human_status when status is None.  Closes celery/celery#2093

flaviogrossi/billiard,djsmith42/billiard,andresriancho/billiard,jakirkham/billiard,pombredanne/billiard,flaviogrossi/billiard,jakirkham/billiard,pombredanne/billiard,djsmith42/billiard,andresriancho/billiard