Don't rely on fontconfig's font composition, but use Emacs's fontset instead.

The former way doesn't works correctly. The secondary font (Japanese
font) specified in ~/.fonts.conf doesn't seem to be recognized by Emacs.

In the latter way, we need to use a hook to create our fontset at the
proper time.
See "https://github.com/tarao/dotfiles/blob/master/.emacs.d/init/window-system.el".
Activate the 'undo-tree' package manually.
Explicitly disable the background of the face magit-item-highlight.