widget type: command?

[raman <raman@google.com>]

I  was surprized to see that in the predefined widget types  we dont
appear to have something for use to  typecheck  user input  for
"interactive-command" -- we have 'function and 'symbol.

I added this to emacspeak -- but it might be nice to get it into
wid-edit with a suitable renaming.
(defun emacspeak-keymap-command-p (s)
  "Check if `s' is suitable to be bound to a key."
  (or (commandp s) (keymapp s)))
;;; rename to either 'command or 'interactive-command 
(define-widget 'ems-interactive-command 'restricted-sexp
  "An interactive command."
  :completions
  (apply-partially #'completion-table-with-predicate obarray 'emacspeak-keymap-command-p 'strict)
  :prompt-value 'widget-field-prompt-value
  :prompt-internal 'widget-symbol-prompt-internal
  :prompt-match 'emacspeak-keymap-command-p
  :prompt-history 'widget-function-prompt-value-history
  :action 'widget-field-action
  :match-alternatives '(emacspeak-keymap-command-p)
  :validate (lambda (widget)
              (unless (emacspeak-keymap-command-p (widget-value widget))
                (widget-put widget :error (format "Invalid interactive command : %S"
                                                  (widget-value widget)))
                widget))
  :value 'ignore
  :tag "Interactive Command")