More informative error when using a 0.10 module

[weavejester]

If an 0.10 module is used on a 0.11 project, the configuration fails on a prep assert that is hard to understand. We can add a better check with a more informative error message, e.g.

:duct.module/logging returned a map when we expect a function.
Perhaps this is an older module, and needs upgrading?