Please add S-tab to button-buffer-map

[Lennart Borgman (gmail)]

Didn't we decide to add S-tab to button-buffer-map? Could someone please 
add this (the binding is the same used in Info-mode-map):

(defvar button-buffer-map
  (let ((map (make-sparse-keymap)))
    (define-key map [?\t] 'forward-button)
    (define-key map [(shift tab)] 'backward-button)
    (define-key map "\e\t" 'backward-button)
    (define-key map [backtab] 'backward-button)
    map)
  "Keymap useful for buffers containing buttons.
Mode-specific keymaps may want to use this as their parent keymap.")