Before, these were not being reliably canceled before the final COMPLETE or
INTERRUPTED notification went out. This moves closing the progress Timer
to a finally block after the Timer is setup, which should hopefully
guarantee the progress reports are always stopped.
This prevents any more progress reports from being sent, in case there is
one pending anywhere. downloaderProgressListener needs to be volatile to
ensure that the two threads are seeing the same values.
This was an omission on my part when putting together the DownloaderService
in !248
18b3a05806