Reallow undo after the end of the game

This now works fine, even if the board has been flipped.  Not sure
what's changed to fix this.
Add a delay between the last move and final flip

Currently, it often seems like the final player has placed a piece
of his opponent's color instead of his own, since after clicking the
piece that is shown placed on the board is the one that is fated to be
there after the final flip. This is confusing and made me think I was
seeing Bug #679137. Add a delay to prevent confusion.