I went crazy again and upgraded my laptop from 32 to 64 bits. This was a rather complex problem, and in retrospect it may have been easier to simply reinstall. But it was a good exercise and a good test of the new multi-arch support, which, I gotta say, works surprisingly well.

A few other people wrote their own procedures already, but I made my own in my wiki (which, incidentally, I am thinking of using to replace this blog which I can't seem to upgrade to even Drupal 7...).