Unique solubility in Mines means that you can massively increase the

Unique solubility in Mines means that you can massively increase the
mine density without (as you would with a conventional random grid
generator) rendering the game completely unplayable. High mine
densities are really good fun, and the point of the presets menu is
to provide people with pre-tested good settings and things they
might not have thought to try for themselves; so here are three
additional presets with high densities.

git-svn-id: svn://svn.tartarus.org/sgt/puzzles@5906 cda61777-01e9-0310-a592-d414129be87e