If the notification policy for auto-updates is set to 'Notify before Install',
we do not download all the necessary installer binaries. Only the bootstrap
installer is downloaded, which is now under 300Kb thanks to some earlier
changes. The correct approach is to download *ALL* files in preparation for
the install and then notify the user that we are ready. This way, there are
no further downloads required after the user accepts the update, and they have
a great install user experience.