Function import is not transitive

[ndw]

In private correspondence, Achim and I concluded that the spec isn't completely clear on whether p:import-functions in a p:library is transitive.

It's complex enough today. If we made it transitive, we'd have to address questions of visibility for imported functions that would make it yet more complex.

I propose that we add prose that explicitly says imported functions are not transitively availble in the steps that import libraries that import functions.

[gimsieke]

Ok

[ndw]

Make the difference between library import clear.