Named expression-style classes should assign that name to their scope

[alangpierce]

decaffeinate is producing the wrong JavaScript based on my CoffeeScript input:

A = class B
console.log(B)

(repl)

I get this output:

const A = class B {};
console.log(B);

Here's what I expect it to be instead:

let B;
const A = B = class B {};
console.log(B);

This is causing the atom tests to fail after decaffeinate.