[racket] syntax-case and multiple ellipsis

> Silly me, I was trying (require syntax/parse). Thanks!

Yeah, if I had a nickel for every time I've forgotten to (require
(for-syntax syntax/parse)) I would be... well, not rich, but able to
buy a fancy coffee. Which if I'd already drank, I probably wouldn't
have made the mistake.

If someone were to inflict a Microsoft Office Clippy on us, one of its
features should probably be, "Hi! It looks like you're writing a
syntax-parse macro!" and offer to fix the require.