Bug#1071668: Add Acquire::Total::Dl-Limit

[Dan Jacobson <jidanni@jidanni.org>]

Package: apt
Version: 2.9.3
Severity: wishlist

apt-transport-http
apt-transport-https
both say

       The used bandwidth can be limited with Acquire::http::Dl-Limit which
       accepts integer values in kilobytes per second. The default value is 0
       which deactivates the limit and tries to use all available bandwidth.
       Note that this option implicitly disables downloading from multiple
       servers at the same time.

That's great. Except when there is a mixture of http and https sources.
(Probably not considered back when there was only http.)

Then to achieve a Dl-Limit=8 we need to do e.g.,

-o Acquire::http::Dl-Limit=4 \
-o Acquire::https::Dl-Limit=4

That indeed never goes past 8 so we are happy.

But lets say after a few minutes the http source is now already fetched,
well the https source is still limited at 4 even though it would be fine
if it became 8.

Therefore there needs to be a
-o Acquire::Total::Dl-Limit=8

Also the "implicitly disables downloading from multiple servers at the
same time" shouldn't apply to the new Acquire::Total::Dl-Limit. Or at
least allow overriding.

Also it would be a good idea to allow overriding "implicitly
disables..." for http and https too.