Allow magit-popup menus to be redefined for iterative development.

magit-redefine-popup.el

(defmacro magit-redefine-popup (name doc &rest args)
  "Define a popup command named NAME.

See magit-define-popup for a description of the parameters.

Unlike with magit-define-popup, changes to the popup definition
*will* be reflected upon re-evaluating this form. This is
convenient for iterative, interactive development of a
magit-popup menu."
  (let* ((-name (symbol-name name))
         (popup-name (progn
                       (string-match "\\([^ ]+\\)-popup" -name)
                       (match-string 1 -name))))
    `(progn
       (makunbound (intern ,(concat popup-name "-arguments")))
       (makunbound (intern ,-name))
       (fmakunbound (intern ,-name))
       (magit-define-popup ,name ,doc ,@args))))