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...
really surprised that you use `EasyBuildMNS` here to generate the error. the person installing only familiar with their own MNS might not understand what the `EasyBuildMNS` naming is about. maybe add both (or report the `EasyBuildMNS` in debug?)