Merged revisions 72167 via svnmerge from

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

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  r72167 | walter.doerwald | 2009-05-01 19:35:37 +0200 (Fr, 01 Mai 2009) | 5 lines

  Make test.test_support.EnvironmentVarGuard behave like a dictionary.

  All changes are mirrored to the underlying os.environ dict, but rolled back
  on exit from the with block.
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