so there's a `annex.web-download-command` settings, great! i have used
it to do bandwidth limitations with:

    wget --limit-rate=$download -O %file %url

...and it works well.. however, i notice the output is different, and
that's because once we override that setting, git-annex doesn't add
other magic settings it uses. so by turning that thing on and off and
inspecting the process list, i was able to figure out that the command
is actually:

    wget -q --show-progress --clobber -c --limit-rate=$download -O %file %url

that gets me closer to the command generated by git-annex. however, i
am not sure the `--clobber` and `-c` flags should always be
present. furthermore, the `--user-agent
git-annex/5.20150610+gitg608172f-1~ndall+1` flag is missing.

could there be an (optional) %useragent interpolation to fix that?

what about the other settings, is it okay to hardcode those?

maybe this would be easier if there would be an options override just
like rsync, but separate ones for curl and wget... --[[anarcat]]
