Hi Dave,
I've tried hacking at the AllowedExtensions variable, and restarting the server. It didn't work out of the box, and it's not working now, unfortunately. I click the "Scan for static pages" link and it opens the URL static/admin/fs-scan-progress, which spits out an essentially blank page (the header is "Filesystem Search", then "Your Workspace : ACS System Wide Administration : Static Pages Admin : Filesystem search", then an hrule, then nothing.)
I am hoping maybe someone has some insight into why this may not be working; I was a reasonable Tcl hacker something like four years ago, but my knowledge of databases is kind of weak and I'm obviously unfamiliar with the nuances of the OpenACS package. Maybe I'll try and spend some time hacking through the package code.
Thanks, everyone, for your help.