Dominosa: rewrite the solver.

Dominosa: rewrite the solver.

The new solver should be equivalent to the previous solver's
intelligence level, but it's more usefully split up into basic
data-structure maintenance and separate deduction routines that you
can omit some of. So it's a better basis to build on when adding
further deductions or dividing the existing ones into tiers.

The new solver also produces much more legible diagnostics, when the
command-line solver is run in -v mode.