Allow a 1-omino to be completely destroyed and recreated in an

Allow a 1-omino to be completely destroyed and recreated in an
arbitrary unclaimed square. This cures the most common cause of
generation failures (covering a large area in dominoes was the most
difficult case, and would fail even if the large area was 1xn!); the
failure rate is now sufficiently low under all circumstances I've
found that I'm willing to just loop until I get a success.

git-svn-id: svn://svn.tartarus.org/sgt/puzzles@7693 cda61777-01e9-0310-a592-d414129be87e