[racket-dev] seeing compile-time error for Whalesong on HEAD

There's something funky in typed-racket/private/type-contract.rkt,
with some non-uniformity in the following lines:

https://github.com/plt/racket/blob/master/collects/typed-racket/private/type-contract.rkt#L143-L149

where the keywords are being called #:kind, but the variable binding
is called "flat", and it's done inconsistently between t->c and
t->c/both, and there's a use here:

https://github.com/plt/racket/blob/master/collects/typed-racket/private/type-contract.rkt#L432

that tries to use them interchangeably, and that looks off.