The MultiUpload extension has been unmaintained
for a while. I believe
its author has moved on to another job. I've written a completely
independent piece of extension code (as a byproduct of work I did for
the WorkingWiki extension) that provides a multiple-upload interface.
After consulting with Petrb, who is listed as the current maintainer of
MultiUpload on
mediawiki.org, I'm thinking of checking in my
multiple-upload code as a new version of MultiUpload, completely
replacing the current implementation.
This is done now.