If you go to e.g. https://sourceforge.net/p/konfidi/code/499/tarball it says its generating (but its not) and it takes a long time (could know instantly) to figure out that there's not a running job.
If there's no file, and no busy/ready task to make one, we know that right away and can just prompt the user to resubmit w/o any delay. In this case, we also should not show a "Generating snapshot..." message when the page loads.
allura:tv/7059
Merged, with some modifications