function _hasJob(id) {
    var job = _jobs[id] || _runningJobs[id] || _waitingJobs[id];
    return job ? __extend(job) : null;
  }
Returns true if a job with the specified id is currently running or
waiting, and false else.

@param  {String}  id The id of the job.
@return {?Object} Returns the job object if it exists.