Our handling of SATISFIES in CTYPEP is too eager: we cannot give a
good answer unless the function is foldable. I am not sure why this
hasn't been a problem earlier, but something between 1.0.12 and 1.0.17
brings this to the fore (I haven't checked yet, but I suspect the
Patch (and test-case) attached. I plan to commit this after the freeze
unless it is felt that this is important enough for thaw.