Allow unbalanced expressions to be closed at point.

I don't like the default behavior for sp-up-sexp when closing expressions.

For example

```lisp
(add-hook 'emacs-lisp-mode-hook
          'emacsmate-smartparens-emacs-mode-hook |
```

Pressing `)` will result in

```lisp

(add-hook 'emacs-lisp-mode-hook)|
          'emacsmate-smartparens-emacs-mode-hook 
```

Where I want

```lisp
(add-hook 'emacs-lisp-mode-hook
          'emacsmate-smartparens-emacs-mode-hook)|
```

This mimics autopair's behavior.