If any of the packages to install has requires a base package, that is
installed in a more general installation location, we copy the package
to the target installation location. Ideally we'd hard-link, but BFS
doesn't support that. Symlinks would be a small nightmare to maintain.
We might want to choose the installation location intelligently
depending on the base package requirement -- e.g. install curl_devel in
system rather than common, since curl is installed in system -- so we
can avoid duplicating packages.
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