[Zope] Add item ZMI dropdown, metatype icons, temp folder contents gone on Zope2.5.1 installation

[Jeff Kowalczyk]

I started up the ZMI this morning and found that the metatype icons in the
ZMI were gone (display as broken images, their URLs seem to be unchanged),
and the whole row with the add-item dropdown is gone, it does not display.
It seems that the metatype system in general got knocked silly on this
installation somehow.

I did copy in a few products this morning (cvs checkouts of Photo, CMFPhoto,
and CVS updates of CMF and Plone), but nothing that I hadn't used before,
and they're hardly fringe products.

Has anyone seen this type of thing before, and have a tip on how to resolve
it before I nuke my installation and start over on monday? I have the
screenshot if anyone wants to see it.