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/blackbox.sav

@@ -0,0 +1,27 @@
+SAVEFILE:41:Simon Tatham's Portable Puzzle Collection
+VERSION :1:1
+GAME    :9:Black Box
+PARAMS  :8:w8h8m5M5
+CPARAMS :8:w8h8m5M5
+SEED    :15:999785320716678
+DESC    :24:c8b9f8528193756b9a2fd24d
+UI      :2:E0
+NSTATES :2:18
+STATEPOS:2:13
+MOVE    :2:F2
+MOVE    :2:F4
+MOVE    :2:F5
+MOVE    :3:F25
+MOVE    :3:F26
+MOVE    :3:F11
+MOVE    :3:F12
+MOVE    :3:F15
+MOVE    :4:T7,7
+MOVE    :4:T7,4
+MOVE    :4:T1,7
+MOVE    :2:F3
+MOVE    :2:F9
+MOVE    :3:F27
+MOVE    :4:T5,7
+MOVE    :4:T1,8
+MOVE    :1:R