Xft drawing leaks

[Stephen J. Turnbull]

Didier Verna writes:

 > Maybe this is already known, but just in case, I've posted a screen shot[1]
 > of my Gnus Group buffer in which I did a mouse sweep over all groups in
 > order to have them displayed as selectable (mouse clickable). The same
 > effect can be achieved with paren-mode's matching paren face.
 > 
 > As you can see, there are residues of the face all over the place...

This is well-known Xft and/or freetype breakage in the computation of
text extents; they don't take antialising "smudging" of the glyphs
into account.  Both GNU Emacs and Firefox suffer from related problems
(Emacs users report the font turd effect, Firefox clips too tightly.)

Patches welcome.