Merged revisions 71881 via svnmerge from

Merged revisions 71881 via svnmerge from
svn+ssh://pythondev@svn.python.org/python/branches/py3k

................
  r71881 | walter.doerwald | 2009-04-25 14:48:43 +0200 (Sa, 25 Apr 2009) | 14 lines

  Merged revisions 71875 via svnmerge from
  svn+ssh://pythondev@svn.python.org/python/trunk

  ........
    r71875 | walter.doerwald | 2009-04-25 14:15:07 +0200 (Sa, 25 Apr 2009) | 7 lines

    Issue #5837: Certain sequences of calls to set() and unset() for
    support.EnvironmentVarGuard objects restored the environment variables
    incorrectly on __exit__.

    Fix this by recording the initial value of each environment variable on the
    first access in set() or unset().
  ........
................