When run by
occ-install-or-update, this procedure will determine if the
curl-timestamp.txt file has changed since the last attempt (if any), and if so, will update the contents of
new-root-url, either by copying all the files listed in the
curl-contents.txt file (from the webserver), if it exists and is non-empty, or else by extracting the contents of the
curl-archive.car file (from the webserver). This is similar to the steps taken by
occ-module-installer for each module.