why is get-gl-attribute not implemented? #33

Hello,

Why is get-gl-attribute not implemented? I'm not necessarily looking for a fix, 
but was just curious when I found the following code in:
lispbuilder-sdl/sdl/video.lisp:

(defun get-gl-attribute (attribute value)
  (declare (ignore attribute value))
  ;; TBD
  )

Thanks again for a great library,
Mick