Doesn't coexist with unattended-upgrades nicely

apt-checkupdates runs before unattended-upgrades, which produces duplicate emails about available updates.

It should run _after_ unattended-upgrades, and only warn about packages that unattended-upgrades doesn't care about (e.g. PPA packages etc.).

Start by locating the cron script's apt-checkupdates entry point and reviewing how it runs relative to unattended-upgrades. Done means it runs afterward, avoids duplicate emails, and reports only packages unattended-upgrades does not handle, such as PPA packages.

Written by the indexing model from the issue text.