Merged revisions 67171 via svnmerge from

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

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  r67171 | benjamin.peterson | 2008-11-08 12:38:54 -0600 (Sat, 08 Nov 2008) | 4 lines

  check for assignment to __debug__ during AST generation

  Also, give assignment to None a better error message
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