Anatol Pomozov authored Mar 26, 2020 and Allan McRae committed May 09, 2020

This is an equivalent of alpm_db_update but for multiplexed (parallel)
download. The difference is that this function accepts list of
databases to update. And then ALPM internals download it in parallel if
possible.

Add a stub for _alpm_multi_download the function that will do parallel
payloads downloads in the future.

Introduce dload_payload->filepath field that contains url path to the
file we download. It is like fileurl field but does not contain
protocol/server part. The rationale for having this field is that with
the curl multidownload the server retry logic is going to move to a curl
callback. And the callback needs to be able to reconstruct the 'next'
fileurl. One will be able to do it by getting the next server url from
'servers' list and then concat with filepath. Once the 'parallel download'
refactoring is over 'fileurl' field will go away.

Signed-off-by: Anatol Pomozov <anatol.pomozov@gmail.com>
Signed-off-by: Allan McRae <allan@archlinux.org>