need a way for downloads with multiple related files

[Martin Pool]

Some people want to host for example an Eclipse plugin repository on Launchpad (see bug 157017). This is just downloadable files, but they need to have particular url relationships to each other:

> I dont' know how an apt repository is, but a Eclipse update-site is
> a folder with the following structure:
>
> site.xml
> plugins/
> a_plugin.jar
> another_plugin.jar
> features/
> a_feature.jar
>

This is possible on eg sourceforge where you can just put them on the web hosting feature.

I can see a couple of ways to do this:
 - make the download files have related urls with a way for the user to make subdirectories
 - support generic web hosting