'--all-users' support incomplete (need to load & save reg hives)

[Explorer09]

This is part of usb_vaccine.cmd to-do list.

Currently usb_vaccine.cmd cannot process registries of all users available on
one's computer, but process only users that are currently logged in. Other user
accounts' registries are not touched.

This issue affects [mountpoints] phase, and all options that start with
--all-users.

We need a mechanism to load and process registry hives, and save back (with
hive backup) when completed. The background information needed to implement
this has been all documented in Technicals.txt. However, it turns out that
implementing this is not easy. We will need a routine to parse reg.exe output,
and a temporary directory for the script to process hives, and perhaps some
reordering of subroutines in main.