Added an additional argument to forkWorkerThread for a push action.
FoundMode --> FoundModeUsingPull
Fixed supervisor bug in FoundModeWithPull.

The supervisor was not always checking the latest
result to see if it satisfied the checking function.
Added lots more fold markers inside forkWorkerThread.
Factored out the new checkpoint computation in forkWorkerThread.
Moved part of compressProgressUpdate into a separate function.
Moved WorkerPushActionFor type family into the Worker module