It turns out I'd been more efficient than I remembered. There are
already text files in Jena, ARQ and other places e.g.
http://jena.svn.sourceforge.net/viewvc/jena/ARQ/trunk/MOVED%20TO%20APACHE.txt
I didn't get a sense of which option people thought was best.
Three choices:
1/ Delete the repository trees. Leave one text file. Need to use
history browsing to see anything. Will very noticeably alert anyone with
a copy currently checked out. (Paolo's first suggestion)
2/ Leave for browsing but delete the build files and other stuff to stop
accidental build and use. (Paolo's second suggestion)
3/ Have a "Jena has moved" file as now, maybe with a longer content than
is currently there. (current situation)
Andy