* Took into account DST when computing localtime zones.  This wasn't accounted for when using non-UTC datetimes with queue.enqueue_at()

* Updates tests with mocked timezones to test both scenarios

... such that it fetch all dependency status using SMEMBERS and HGET rather than SORT.

1) Check if `created_at` when checking if dependencies are met.

   If `created_at` is `None` then the job has been deleted. This is sort of hack - we just need one of the fields on the job's hash that is ALWAYS populated. You can persist a job to redis without setting status...

2) Job#fetch_dependencies no longer raises NoSuchJob.

   If one of a job's dependencies has been deleted from Redis, it is not returned from `fetch_dependencies` and no exception is raised.

Convert method on Job to return a boolean and rename. Also use
fetch_many in Queue#enqueue_dependents.