Leave move list of game position on stack permanently

Leave move list of game position on stack permanently

The move list that was temporarily created for ParseMove and Highlight
is now kept permanently on the stack (by setting msp to the end of it
after it is created). ParseMove and Highlight thus no longer have to
generate it, and generation is moved to the top of the main loop, and
only done when the list does not exist yet. The list is discarded as soon
as we execute a command that changes the game position.