add debug-level logging to FutureTransfer.listenFor

log all of the detailed progress events that are sent to the progress listener, as well as logging the means by which the `Promise` is completed (how the inherent race condition resolves).
minor: update the scratch code to test FutureTransfer
Merge pull request #21 from pellucidanalytics/topic/s3-progress-logging

add debug-level logging to FutureTransfer.listenFor