Merged revisions 81897-81898,81902 via svnmerge from

Merged revisions 81897-81898,81902 via svnmerge from
svn+ssh://pythondev@svn.python.org/python/branches/py3k

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  r81897 | mark.dickinson | 2010-06-11 17:56:34 +0100 (Fri, 11 Jun 2010) | 1 line

  Avoid possible undefined behaviour from signed overflow.
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  r81898 | mark.dickinson | 2010-06-11 20:05:08 +0100 (Fri, 11 Jun 2010) | 1 line

  Fix an incorrect return type.
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  r81902 | mark.dickinson | 2010-06-11 20:50:30 +0100 (Fri, 11 Jun 2010) | 1 line

  Fix more undefined-behaviour inducing overflow checks in struct module.
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