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...
there's no reason to keep backward compatibility here, nobody should be affected directly, and this change will be clear in the release notes, yes

the `_mns` is really needed here, having multiple modules with an `easybuild` name thoroughly screws things up...