Patch from Debian, to bring the use of the X selection/clipboard in

line with freedesktop.org. (This is relatively simple for Puzzles,
since it only writes to the clipboard and never reads it, so the
question of which selection to use when is most easily dealt with by
always writing to both.)

git-svn-id: svn://svn.tartarus.org/sgt/puzzles@8929 cda61777-01e9-0310-a592-d414129be87e