Apparently, some pixels from the close button on the window image were
missing from the Non-opaque image, they have been added in the XPM file
which was then converted to TIFF with ImageMagick's command:
convert -depth 8 -compress lzw xpm/nonopaque.xpm tiff/nonopaque.tiff
to have a file similar to what was there before
Signed-off-by: Christophe CURIS <christophe.curis@free.fr>