New puzzle: `Slant', picked from the Japanese-language section of

New puzzle: `Slant', picked from the Japanese-language section of
nikoli.co.jp (which has quite a few puzzles that they don't seem to
have bothered to translate into English).

Minor structural change: the disjoint set forest code used in the
Net solver has come in handy again, so I've moved it out into its
own module dsf.c.

git-svn-id: svn://svn.tartarus.org/sgt/puzzles@6155 cda61777-01e9-0310-a592-d414129be87e