parse all options when detached

Issue: 
All command-line options after '--'  are ignored in 'detach mode. 

$ celery worker --detach-n w1  -A myapp -c 8  -- celeryd.prefetch_multiplier=16
[2014-01-09 14:56:10,097: DEBUG/MainProcess] basic.qos: prefetch_count-> 32

$  celery worker --detached -n w1  -A myapp -c 8  -- celeryd.prefetch_multiplier=16
[2014-01-09 14:57:30,766: DEBUG/MainProcess] basic.qos: prefetch_count->128