* run_after、grabbed_untilを見て処理を行う
* simplejsonだけでなくpickleも使える様に
* Server.pyの実装

未実装:
  Schwartz.py
    __init__
      verbose
	  prioritize
	  driver_cache_expiration
	  retry_seconds

    list_jobs
	lookup_job
	set_verbose
	work_until_done
	work_on
	find_job_with_coalescing_prefix
  Client.py
    list_jobs
	lookup_job
	set_verbose
    set_prioritize
	get_server_time