Note that, if an url is added to the web log for such a remote, it's not
distinguishable from another url that might be added for the web remote.
(Because the web log doesn't distinguish which remote owns a plain url.
Urls with a downloader set are distinguishable, but we're not using them
here.)
This seems ok-ish.. In such a case, both remotes will try to use both
urls, and both remotes should be able to.
The only issue I see is that dropping a file from the web remote will
remove both urls in this case. This is not often done, and could even
be considered a feature, I suppose.