Require 'tree-widget instead of 'wid-edit.

Require 'tree-widget instead of 'wid-edit.
(recentf-filename-handler): Fix widget :type.
(recentf-cancel-dialog, recentf-open-more-files)
(recentf-open-files-action): Doc fix.
(recentf-dialog-goto-first): New function.
(recentf-dialog-mode-map): Set parent keymap first.
(recentf-dialog-mode): Define with define-derived-mode.  Don't
display continuation lines in dialogs.
(recentf-edit-list): Rename from recentf-edit-selected-items.
(recentf-edit-list-select): Rename from recentf-edit-list-action.
Simplify.
(recentf-edit-list-validate): New function.
(recentf-edit-list): Update accordingly.
(recentf-open-files-item-shift): Remove.
(recentf-open-files-item): Convert menu elements into tree and
link widgets.  Don't create the widgets.
(recentf-open-files): Update accordingly.
(recentf-save-list): Untabify.