Merged revisions 79936 via svnmerge from

svn+ssh://pythondev@svn.python.org/python/trunk

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  r79936 | philip.jenvey | 2010-04-10 15:27:15 -0500 (Sat, 10 Apr 2010) | 3 lines

  fix PYTHONWARNINGS handling to not modify the original env value and improve
  its tests
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