Merged revisions 84258,84268 via svnmerge from

Merged revisions 84258,84268 via svnmerge from
svn+ssh://pythondev@svn.python.org/python/branches/py3k

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  r84258 | antoine.pitrou | 2010-08-22 12:18:36 +0200 (dim., 22 août 2010) | 4 lines

  Test that calls to path hooks and meta_path entries are serialized by the import lock.
  (part of issue #9251)
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  r84268 | antoine.pitrou | 2010-08-22 22:43:26 +0200 (dim., 22 août 2010) | 4 lines

  Add an import lock test for multithreaded circular imports.
  (part of #9657)
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