bugfix/7443-persistent-files-permission fixes a potentially important
security issue with permissions on persistent files.
Everything works fine for me, *but* one should run the test suite to
check that the new regression tests are good (#7460). I'm not sure
I'll have time + access to the right electricity+network setup needed
to run the test suite by the freeze (July 1st), so if anonym was so
kind to do it before merging, this would be just great. I can fix the
regression tests later.
