Unnecessary downloads

[geoffklee]

The processor is technically idempotent, insofar as it won't recreate a package if the output package already exists; however, before it determines whether the output package exists, it will download the ISO or DMG if it doesn't exist.

What should happen:

if package_exists:
    continue
elif download_exists:
    make_package
    continue
else:
    download
    make_package
    continue

Because of the way the helper script has grown organically, making it work like this will take a bit of refactoring which, currently, I'm leaving for another day.