These are necessary because the argument to a ctype function cannot be
a negative value unless it's EOF. Thanks to Cygwin gcc for pointing
out the mistake, and to Patrick Shaughnessy for this patch.
A user pointed out that if you construct a 'solution' in which no clue
square has too _many_ borders but at least one has too few, and then
bring those clues up to their count by adding extra stray border lines
_inside_ a connected component (avoiding actually dividing any
component completely into two), then the game checker treats that as
solved for victory-flash purposes, on the grounds that (a) the grid is
divided into components of the right size and (b) all clues are
satisfied.
A small example is 4x4n4:22a2b2c33, with the non-solution of dividing
the grid into four 2x2 square blocks and then adding a spurious extra
edge between the two 3 clues. The old Palisade completion check would
flash for victory _at the same time_ as highlighting the spurious edge
in COL_ERROR.
Fixed by enforcing in is_solved() that every border line must separate
two distinct connected components.
The solve move stored in 'aux' by new_game_desc consists of printable
characters in the range '@' to 'O', each representing a 4-bit bitmap
of edges around a cell. But the one generated on the fly by
solve_game() was missing out the 0x40 bit and just returning
characters in the range ^@ to ^O - which would not only have been
horrible if you found such a string in a save file, but also meant
that a game with any completely borderless square would have a
solution move string terminating early due to the ^@, causing
execute_move() to reject it.
Example: ./palisade --test-solve --generate 1 5x5n5#12345-37 now
succeeds, where previously it failed an assertion.
