bug#21202: 24.5; minor mode lighter freezes emacs

[Leo Liu]

Be carefully with the following steps; you might have to force-kill
emacs.

1. (define-minor-mode ifreeze () :lighter (:propertize " IF" error))
2. M-x ifreeze

Made a typo there in the :lighter and was surprised to see no amount of
C-g can save emacs :(

Leo