Merged revisions 64309 via svnmerge from

Merged revisions 64309 via svnmerge from
svn+ssh://pythondev@svn.python.org/python/trunk

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  r64309 | amaury.forgeotdarc | 2008-06-16 21:12:42 +0200 (lun., 16 juin 2008) | 8 lines

  Issue 3110: Crash with weakref subclass,
  seen after a "import multiprocessing.reduction"

  An instance of a weakref subclass can have attributes.
  If such a weakref holds the only strong reference to the object,
  deleting the weakref will delete the object. In this case,
  the callback must not be called, because the ref object is being deleted!
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