Diagnose obsolete recipes.

[sageserpent-open]

This follows in from #72.

The situation here is that as test case synthesis code evolves, recipes can become invalid and cause either an exception deep in the Americium implementation that is mystifying to the user, or can silently produce the wrong test case.

What is needed is some kind of consistency check that detects the obsolescence and produces a nice diagnostic.

If that isn't possible, at least detecting the exception and relabelling with a nice diagnostic would be an improvement, although there is a danger that this will simply cover up bugs in Americium.