Bring back the old lock query for older versions of Mongo.
Bring back the old lock query for older versions of Mongo.

kierangraham/delayed_job_mongoid,collectiveidea/delayed_job_mongoid,mvoloz/delayed_job_mongoid,amw/delayed_job_mongoid,davidrv/delayed_job_mongoid,matekb/delayed_job_mongoid,Guidecase/delayed_job_mongoid,dblock/delayed_job_mongoid