Fix taking effect of some option changes

Fix taking effect of some option changes

This fixes a bug reported at Ubuntu: when switching off move highlighting
in Two Machines mode, the last move before the switch stayed highlighted.
The GeneralOptionsOK() now clears any remaining highlights when highlighing
is off. Similar problems with blind-fold mode and coordinates, which require
a total board redraw to take effect, are now solved by also forcing such a
redraw in GeneralOptionsOK() when they change.