On image-mode-winprops and using image-mode elsewhere

[Mark Oteiza]

I've been poking image-dired lately and wanted to use the navigation
commands implemented in image-mode in image-dired-display-image-mode.
This should be as simple as setting a keymap parent, but I am greeted
with

  (wrong-type-argument listp t)

which appears to me to be due to 83600dc. In particular, the line

  (defvar-local image-mode-winprops-alist t)

but I think this should be nil.  Thought I'd ask before I change it.