fix: inputs/.geoscrub/geoscrub_output/geoscrub.csv.run: make(): added warning that this will truncate the geoscrub database tables

/README.TXT: to back up the local machine's hard drive: just do a single pass, to avoid the numerous different steps

backups/*retention_policy*: on jupiter: changed to avoid retaining backups further back, as these consume significant disk space on jupiter and are not useful for anything

fix: lib/sh/local.sh: $sync_remote_url: need $USER so user can be overridden when running as root

fix: /README.TXT: to back up the local machine's settings: to jupiter: need `sudo -E` for new Documents/BIEN/vegbiendev*/

/README.TXT: backups of ~/.dropbox/: just pause and resume Dropbox instead of quitting and restarting it

/README.TXT: to back up the local machine's settings: to Dropbox: exclude gmvault-db/ to save space in Dropbox

/README.TXT: to back up the local machine's settings: don't need to exclude ~/Library/Thunderbird/Profiles/9oo8rcyn.default/global-messages-db.sqlite because the disk that was corrupting this file has been replaced (#907)

/README.TXT: to back up e-mails: don't need to also sync aaronmk@nceas.ucsb.edu because these e-mails are also in aaronmk.nceas@gmail.com (auto-forwarded)

/README.TXT: Notes on system stability: removed no longer applicable warning about system upgrades, which is now incorrect because the disk space overrun bug (#887) was found not to have been caused by a system upgrade