Bring Pearl's game-completion handling in line with my usual practice:

Bring Pearl's game-completion handling in line with my usual practice:
the 'completed' flag is not reset if you make a new move transforming
a solved game into an unsolved state, so the game won't flash again if
you manually erase and redraw a line segment (though it still will if
you undo and redo past the first solved state in the undo history).

[originally from svn r9750]