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...
As a side remark: if we want git/svn/... support to fetch files, we need some serious change to the ```fetch*``` functions. It would be a good idea to do those together.