Bug fix: Icon not painted correctly when window is upscaled

- Fix a bug that icon is not painted correctly when window is upscaled.
  Modify clientwin_repaint() to use mini-window-space rectangle.

- Fix a bug that ps->o.showUnmapped is ineffective for windows unmapped
  after skippy-xd starts.

- Modify clientwin_repair() to avoid repainting due to window content
  changes when icon/filled content is displayed.

- Enable ps->o.xineramaShowAll by default.

- Code clean-up.