Until now, Same Game has been the only puzzle in this collection

which is unable to guarantee that every grid it generates can be
solved. So I'm eliminating that exception: this checkin contains a
more sophisticated grid generator which does guarantee solubility.
It's a bit slow (most noticeably on the 15x10c3 preset), and the
quality of the generated grids is slightly weird (a tendency toward
small regions rather than large sweeping areas of contiguous
colour); however, I'm willing to see the latter as a feature for
now, since making the game more challenging while simultaneously
guaranteeing it to be possible sounds like an all-round win to me.

From now on I'm raising my standards for contributions to this
collection. I made this fix to Same Game because I heard a user
_automatically assume_ that any puzzle in my collection would not be
so uncouth as to generate an impossible grid; as of this checkin
that's actually true, and I intend to maintain that standard of
quality henceforth.

(Guaranteeing a _unique_ solution is more of an optional extra,
since there are many games for which it isn't a meaningful concept
or isn't particularly desirable. Which is not to say that _some_
games wouldn't be of unacceptably low quality if they failed to
guarantee uniqueness; it depends on the game.)

[originally from svn r6124]

puzzles.but

@@ -959,11 +959,6 @@ Removing a region causes the rest of the grid to shuffle up:
 blocks that are suspended will fall down (first), and then empty
 columns are filled from the right. 
 
-The game generator does not try to guarantee soluble grids;
-it will, however, ensure that there are at least 2 squares of each 
-colour on the grid at the start (and will forbid custom grids for which
-that would be impossible).
-
 Same Game was contributed to this collection by James Harvey.
 
 \H{samegame-controls} \i{Same Game controls}
@@ -1009,6 +1004,23 @@ any points at all. With the alternative \q{(n-1)^2} system, regions of
 two squares score a point each, and larger regions score relatively
 more points.
 
+\dt \e{Ensure solubility}
+
+\dd If this option is ticked (the default state), generated grids
+will be guaranteed to have at least one solution.
+
+\lcont{
+
+If you turn it off, the game generator will not try to guarantee
+soluble grids; it will, however, still ensure that there are at
+least 2 squares of each colour on the grid at the start (since a
+grid with exactly one square of a given colour is \e{definitely}
+insoluble). Grids generated with this option disabled may contain
+more large areas of contiguous colour, leading to opportunities for
+higher scores; they can also take less time to generate.
+
+}
+
 
 \C{flip} \i{Flip}