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/pattern.sav

@@ -0,0 +1,30 @@
+SAVEFILE:41:Simon Tatham's Portable Puzzle Collection
+VERSION :1:1
+GAME    :7:Pattern
+PARAMS  :5:10x10
+CPARAMS :5:10x10
+DESC    :67:4.3/2.2/1.4/3.2/2.3.2/4/6/6/3.1/1/1.1.4/1.1.3/3.3/2.3/6/5/4/1.1/5/5
+NSTATES :2:23
+STATEPOS:2:23
+MOVE    :8:F6,4,1,2
+MOVE    :8:F7,4,1,2
+MOVE    :8:F4,4,2,1
+MOVE    :8:E0,4,2,1
+MOVE    :8:F0,0,1,4
+MOVE    :8:F5,5,1,1
+MOVE    :8:E0,5,3,1
+MOVE    :8:F2,6,1,4
+MOVE    :8:E1,7,1,1
+MOVE    :8:E3,7,1,1
+MOVE    :8:F3,6,1,1
+MOVE    :8:E6,6,4,1
+MOVE    :8:F6,0,1,4
+MOVE    :8:F7,0,1,5
+MOVE    :8:E6,6,1,3
+MOVE    :8:E7,7,1,3
+MOVE    :8:E6,9,1,1
+MOVE    :8:F0,7,1,2
+MOVE    :8:F1,8,4,1
+MOVE    :8:E5,8,1,1
+MOVE    :8:F3,9,1,1
+MOVE    :8:F4,9,1,1