Don't you think the compiler might be upset if I'd forgotten to include the library? That is, after all, one of the benefits of using a statically typed language like C#.
Anyway, I'm pleased to report that I have, at long last, had a somewhat successful(*) run with the Lightning provider. The process was rather non-intuitive (and I say that as an experienced developer of >30 years and a C# developer of ~15 years, so please don't think I'm making noob mistakes here). So that others can avoid my pain, I have written up the steps required as a blog post:
http://tigra-astronomy.com/blog/the-wel ... -core-apps
The final step I was missing was the manual modification of the Package.appxmanifest file.
(*) And wouldn't you just know it, there is a showstopper bug in the I2C Provider!! Basically, if you set the bus speed to "Standard" it goes at 168KHz instead of the specified 100KHz, and standard mode devices (the one I'm using anyway) can't handle that and it produces garbage results
Issue created on GitHub. https://github.com/ms-iot/BusProviders/issues/21