[gnome-chess] Fix failure to detect past threefold repetitions

[Michael Catanzaro <mcatanzaro src gnome org>]

commit 4cabc410857685cfa2e27dc32572ee3e96480f68
Author: Michael Catanzaro <mcatanzaro gnome org>
Date:   Sun Aug 11 12:23:56 2013 -0500

    Fix failure to detect past threefold repetitions
    
    It's not enough to check if the current board state has been repeated
    three times.  We don't end games automatically for threefold repetition,
    so it's possible to play past it.  Calling the draw at any point
    afterward should work.

 src/chess-game.vala |   21 ++++++++++++++-------
 1 files changed, 14 insertions(+), 7 deletions(-)
---
diff --git a/src/chess-game.vala b/src/chess-game.vala
index c2a8f37..f65815e 100644
--- a/src/chess-game.vala
+++ b/src/chess-game.vala
@@ -1528,18 +1528,25 @@ public class ChessGame
 
     private bool is_three_fold_repeat ()
     {
+        foreach (var state in move_stack)
+        {
+            if (state_repeated_times (state) >= 3)
+                return true;
+        }
+
+        return false;
+    }
+
+    private int state_repeated_times (ChessState s1)
+    {
         var count = 1;
 
-        foreach (var state in move_stack.next)
+        foreach (var s2 in move_stack)
         {
-            if (current_state.equals (state))
-            {
+            if (s1 != s2 && s1.equals (s2))
                 count++;
-                if (count >= 3)
-                    return true;
-            }
         }
 
-        return false;
+        return count;
     }
 }