Store game down flag in the game table

This avoids the silly opening of downfil all the time.

For what it's worth, it also makes the information visible in xdump,
as new game selector down.

src/lib/common/game.c

@@ -51,7 +51,7 @@
 #include "server.h"
 
 /*
- * Disable updates
+ * Enable / disable updates
  */
 void
 game_ctrl_update(int enable)
@@ -71,6 +71,27 @@ updates_disabled(void)
     return getgamep()->game_upd_disable;
 }
 
+/*
+ * Enable / disable play
+ */
+void
+game_ctrl_play(int enable)
+{
+    struct gamestr *game = getgamep();
+
+    game->game_down = !enable;
+    putgame();
+}
+
+/*
+ * Is playing enabled?
+ */
+int
+game_play_disabled(void)
+{
+    return getgamep()->game_down;
+}
+
 /*
  * Notice that a player broke sanctuary.
  * This starts the Empire clock if it hasn't been started yet.