New mechanism for automatic generation of the puzzle screenshots on

the web, which I hope will also end up being extended to generate
both Windows and X icons for each individual puzzle. The mechanism
is: for each puzzle there's a save file in the `icons' subdirectory
showing a game state which I think is a decent illustration of the
puzzle, and then there's a nasty set of scripts which runs each
puzzle binary, loads that save file, grabs a screenshot using xwd,
and munges it into shape.

In order to support this I've added two new options (--redo and
--windowid) to all the GTK puzzles, which I don't expect ever to be
used outside the icons makefile. I've also added two more options
(--load and --id) which force a GTK puzzle to treat its command-line
option as a save file or as a game ID respectively (the previous
behaviour was always to guess, and sometimes it guessed wrong).

[originally from svn r7014]

icons/solo.sav

@@ -0,0 +1,36 @@
+SAVEFILE:41:Simon Tatham's Portable Puzzle Collection
+VERSION :1:1
+GAME    :4:Solo
+PARAMS  :3:3x3
+CPARAMS :3:3x3
+DESC    :73:a2e9a5b6a2b3_7a1_4a9_6a2b4_1a7_2b1_7e6_9b2_5a8_1b6a5_9a3_8a7_2b8a6b1a1e4a
+NSTATES :2:29
+STATEPOS:2:29
+MOVE    :6:R7,1,1
+MOVE    :6:R4,6,1
+MOVE    :6:R5,0,1
+MOVE    :6:R0,0,4
+MOVE    :6:R2,0,6
+MOVE    :6:R1,2,3
+MOVE    :6:R0,3,9
+MOVE    :6:R1,3,5
+MOVE    :6:R2,4,8
+MOVE    :6:R0,5,3
+MOVE    :6:R1,5,6
+MOVE    :6:R1,6,4
+MOVE    :6:R4,7,4
+MOVE    :6:R7,6,2
+MOVE    :6:R7,7,5
+MOVE    :6:R8,8,6
+MOVE    :6:R7,3,3
+MOVE    :6:R8,3,7
+MOVE    :6:R8,3,8
+MOVE    :6:R6,4,5
+MOVE    :6:R7,5,7
+MOVE    :6:R8,5,4
+MOVE    :6:R7,2,8
+MOVE    :6:R8,0,5
+MOVE    :6:R4,2,5
+MOVE    :6:R4,3,6
+MOVE    :6:R5,4,4
+MOVE    :6:R4,5,9