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...
OK, the `AttributeError` *is* still needed, it'll still occur whenever the `det_toolchain_*` functions are used (since they do still require the `ec.toolchain` that provides a `Toolchain` instance)