Bug#778873: apt: make /etc/cron.daily/apt (and it's options) runnable more than daily

[Marian Sigler <m@qjym.de>]

I would like to push this. Updates just every day is just horrible,
especially for servers.

Of course, there's other ways like dumping some `apt update` inside
/etc/cron.hourly, but this doesn't do locking etc, so it would be cool
if the "daily" script could be used for this.


As for the "how":
> One solution wrt to the current definition of the options (which should
> of course remain backwards compatible with respect to the "day" unit)
> would be that each option get's an corresponding unit-option which
> defaults to "1 day"
> so e.g. for APT::Archives::MaxAge
> there would be a corresponding
> APT::Archives::MaxAge::Unit, which defaults to say 86400s and
> internally the script works with 1s resolution.
I think this is a bad idea. It would make the significance of one option
depending on another one. I think a better (and easier to implement,
probably) way would be to allow non-integer values for this option - an
update roughly every two hours could be configured by setting this to
"0.1". (Alternatively, unit suffixes such as 2h, 30m, ... could be
implemented)