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/loopy.sav

@@ -0,0 +1,121 @@
+SAVEFILE:41:Simon Tatham's Portable Puzzle Collection
+VERSION :1:1
+GAME    :5:Loopy
+PARAMS  :7:7x7r0dh
+CPARAMS :7:7x7r0dh
+SEED    :15:206083918429411
+DESC    :31:02g222b3b2e2a2b322b2a2a3a2a1d1b
+NSTATES :3:113
+STATEPOS:2:75
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