Having one of these makes it much easier to debug what's going on when
the solver can't solve something. Also, now the solver can grade the
difficulty of a puzzle, it's useful to expose that feature in a
command-line tool.

One of these days I should sit down and work out exactly when a run of
autoconf generates an autom4te.cache directory, and why it can
suddenly turn up unexpectedly one day after years of never needing to
put it in .gitignore!

I've made the existing optional solver diagnostics appear as the
verbose output of the solver program. They're not particularly legible
at the moment, but they're better than nothing.

OS X is beginning to show a warning when a 32-bit application is
opened, so it's high time that this gets enabled. Fix a clang warning
exposed by this build.

Based on a web game I saw a few years ago, and dashed off this weekend
after I thought of a way to write a good (though not quite optimal)
heuristic solver, here's a random little thing not quite in the same
line as the most usual kind of Puzzles fare: instead of making you
scratch your head to find any move to make at all, it's easy to find
solutions in principle, and the challenge comes from having to do so
within a move limit.