uncomment-region-function for #; sexp comments

UPDATE: This description is no longer true. See next comment.

Not sure if anything can be done about this, but I thought it was interesting behavior.

Using emacs `M-x uncomment` to remove a `#;` removes the comment, but also deletes the closing parens. For example:

``` racket
#;(define (f x) x)
```

becomes

``` racket
(define (f x) x
```
