[queue] Do not repeat jobs that yield an error
[queue] [fix] Pass the queue to and from autosave and repeat helpers
[http] [fix] The "json" option for the request method can be of any type
[queue] If autosave is turned off, execute callbacks in push/shift/extend/take on the next tick
[queue] Add unshift method
[queue] Enable recovery of in-progress elements if the process is killed during processing
[queue] [minor] Remove remark on queue datatype optimization, as it is definitely negligible compared to persistence overhead
[queue] [test] Test for modifying queue during execution while backed by local couchdb