[slim-vim] Fix Vim's () matching for Lisp

[Brad Beveridge]

Here is a little task that can be done in isolation.  I ran into this
the other day, the following Lisp form will give Vim's paren matching
(as it currently is) a nightmare

(defun broken ()
  (let ((a 0))
     ;(if a  - parens in comments will be broken
     (if (char= a #\()   ; the characters #\( and #\) will screw Vim up

So if you ever need to work with literal #\(, #\) or put partial forms
in comments then you will screw up Vim's paren matching.  Fixing this
would be a nice little job.

Cheers
Brad