bug#20268: 25.0.50; pcase-lambda broken

[Drew Adams]

> I.e. the code you'd have written without pcase-let would have been
> 
>       (let ((a (foo))
>             (b (car foo))
>             (c (nth 2 foo)))
> 
> which would naturally turn into a pattern like `(,b ,_ ,c)

Just out of curiosity, what was the reason we didn't go in the
direction of Common Lisp's `destructuring-bind' etc., which would
let you write just (a b c) instead of `(,b ,_ ,c)?