fix draw-rectangles (part 1)
fix draw-rectangles (part 1)

 * draw-rectangles has (had?) many bugs that were preventing it from
   working right. First, in fixing what will become part 2 to this
   series, there was no rectangle drawing at all. Turns out things
   in that part were "fixed" but we were sending a vector the CLX
   backend's medium-draw-rectangles* function, which was doing a loop
   for on by #'cddddr. Much to my surprise, rather than throwing an
   error, that just returns nil if the sequence you're looping over is
   a vector instead of a list. So... make medium-draw-rectangles* work
   properly on a vector.

 * of course that wasn't the end of the story as there was a typo in
   the original code that miscalculated the y2 coordinate of every
   rectangle, so all the rectangles extended to the bottom of the
   window. Fixed.

slyrus/mcclim,slyrus/mcclim