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]

midend.c

@@ -740,6 +740,17 @@ void midend_redraw(midend *me)
     }
 }
 
+/*
+ * Nasty hacky function used to implement the --redo option in
+ * gtk.c. Only used for generating the puzzles' icons.
+ */
+void midend_freeze_timer(midend *me, float tprop)
+{
+    me->anim_pos = me->anim_time * tprop;
+    midend_redraw(me);
+    deactivate_timer(me->frontend);
+}
+
 void midend_timer(midend *me, float tplus)
 {
     int need_redraw = (me->anim_time > 0 || me->flash_time > 0);