support for hierarchical module naming schemes

@geimer: this should fix the problem that's blocking you right now

I might need to figure out one more thing w.r.t. the devel module name before this really works for you, I'm looking into that...
`setvar` should be used, yes, but we're not enforces that yet; for now, it's not important, since we only rely on `setvar` for consistent logging, for now

In the future however, I would like to look into supporting a `--record` cmdline option, that produces a simple-ish bash script to show how the installation was performed. Tracking setting/unsetting of env vars will be key in that context, so then maybe we'll have to wrap `os.environ`... Not now though. ;)