Merged revisions 83096 via svnmerge from

Merged revisions 83096 via svnmerge from
svn+ssh://pythondev@svn.python.org/python/branches/py3k

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  r83096 | ronald.oussoren | 2010-07-23 17:05:35 +0100 (Fri, 23 Jul 2010) | 13 lines

  Ensure that sys.prefix can reliably be found
  on OSX. This fixes a small issue that was exposed
  by running test_subprocess through regrtest (and
  hence in a subdirectory).

  Without this patch running python.exe from the
  build tree will fail when these tree conditions
  are true:
  1) the CWD is not the root of build tree
  2) python.exe is found through $PATH
  3) the framework is not yet installed
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