(wl-biff-init-icons, wl-plugged-init-icons): Refer to `display-mouse-p' and

(wl-biff-init-icons, wl-plugged-init-icons): Refer to `display-mouse-p' and
`display-graphic-p'.
(wl-folder-init-icons): Don't search for XBM or the other files.
(wl-plugged-set-folder-icon): Make icons if and only if `display-graphic-p'
returns non-nil.
(wl-highlight-plugged-current-line): Use `before-string' overlay property to
show icon images.
(wl-highlight-folder-current-line): Ditto.
(wl-e21-highlight-folder-group-line): Ditto.
(wl-e21-highlight-folder-by-numbers): Ditto.
(wl-e21-insert-image): Removed.
(wl-e21-setup-*-toolbar): Refer to `display-graphic-p'.
(wl-e21-make-toolbar-buttons): Set the value that Emacs itself said.
(wl-e21-switch-toolbar-after-make-frame): Renamed from
`wl-e21-force-switch-toolbar'.
(wl-e21-make-icon-image): Removed.
(wl-e21-setup-toolbar): Don't search for XBM files.
(wl-use-toolbar): Don't refer to `display-graphic-p' to determine the default
value.