wrong permissions for /tmp/.X11-unix

[Vincent Lefevre <vincent@vinc17.org>]

The last few times I booted my PowerBook, I couldn't start X because of
the following error:

  X: /tmp/.X11-unix has suspicious ownership (not root:root), aborting.

I can fix the permissions manually, but why are the permissions wrong?
How can I fix this permanently?

-- 
Vincent Lefèvre <vincent@vinc17.org> - Web: <http://www.vinc17.org/> - 100%
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Work: CR INRIA - computer arithmetic / SPACES project at LORIA