this patch fixes subpixel highlighting.  it also elimintes the read from
the screen's memory to draw the new text.  on many new graphics cards
(e.g. nvidia.) this improves draw performance.  commented out are two
 lines that also address this problem, but they cause
some flicker.

the new function is somewhat large due to the fact that there are really 5
regions to draw.  (1) unhighlighted boxes (2) one partially highlighted box
(3) 0-n highlighted boxes (4) 0,1 partially highlighted box (may be the same
box as 2) (5) 0,n unhighlighted boxes.  

frdrawsel0 does a similar but inverse, redrawing the background but not the
text.