Three Dollar Quill

I ground through the tests in Impliciula, getting them to pass, although probably also making them not as good at catching mutations. I'll work on that once I've managed to get the coverage up. And I'll consider that once I've updated the remainder of the tests.

See, a bunch of the System F tests have this pattern of "check one expression against the inferred type of another", and I need to take some time to decide whether to bash together a helper function to deal with the whole "they're generators now" thing, or to "simply" work out the actual type they should have, and check against both of them separately.

I'm not going to make a decision right now, because I'm still really tired and stuff and I want to get to bed.

Good night.