* wl-e21.el (wl-highlight-folder-current-line): Use Posix style character

* wl-e21.el (wl-highlight-folder-current-line): Use Posix style character
 classes and Perl style shy-groups for regexp.
(wl-highlight-plugged-current-line): Use Posix style character classes for
 regexp.
(wl-e21-highlight-folder-by-numbers): Ditto.
(wl-e21-display-image-p): Use `display-images-p' instead of
 `display-graphic-p'.
(display-images-p): Make an alias to `display-graphic-p' if it is not
  available.  It is for Emacs version prior to 21.0.105.

* wl-demo.el (wl-demo): Use `display-images-p' instead of `display-graphic-p'.
(wl-demo-image-type-alist): Ditto.
(display-images-p): Make an alias to `display-graphic-p' if it is not
 available.  It is for Emacs version prior to 21.0.105.