[reversi] Rename to "Reversi" from "FD Reversi".
[duim,gtk] Don't need to reset color.

We destroy the context immediately, so no need to change the
color back.
[duim,gtk] gcontext is a CairoContext, not GdkGC.
[duim,gtk] Some initial color support.
[duim,gtk] Set a background color for clear-box.

I'm not sure if this is right, as it might be handled by
the caller.