Update regarding this issue:
Brion had sourceforge begin a conversion of our cvs repository as described here: https://sourceforge.net/docs/E09 . After that I downloaded our cvs tarball and tried to convert it to a subversion dump locally with the steps described here: http://kohl.wikimedia.org/~avar/cvs2svn . As you can see there's a slight corruption in our repository which the sourceforge conversion presumably stopped on (bug report filed by Brion here: https://sourceforge.net/tracker/index.php?func=detail&aid=1407846&gr... )
Having solved that I proceeded to import my local dump into a subversion repository using the bdb filesystem, running into another issue: http://kohl.wikimedia.org/~avar/svn2bdb (bug report filed by me here: https://sourceforge.net/tracker/index.php?func=detail&aid=1407877&gr... ), I then tried again with the fsfs filesystem which worked, but there might still be some corruption.
Anyway I have my own publically accessable "fork" of the MediaWiki repository available now at http://avar.lir.dk/mw_svn/ It's publically +rw so feel free to play around with it if only to learn how subversion operates. As a tribute to our two previous forks it's called Ænotifwiki and you can only commit to it if you promise to obey my coding style which is that you must use negative indentation, code must be right-aligned at the 80th column. Also, all comments have to be in either Hungarian or Klingon.
= Statistics 874M svn dump file 176M unpacked cvs repository 284M fsfs filesystem # of files in the fsfs filesystem: 25454
= How to get it running:
$ svn co http://avar.lir.dk/mw_svn/trunk/phase3
or
$ svn co http://avar.lir.dk/mw_svn/trunk
for the whole thing
then just modify something, "svn diff file" (no -u) and "svn ci file"
and of course there's other neat svn stuff, like every commit getting a single revision (no more per-file-revisions,just try svn diff -r12716:12717) and file properties etc.