Merged revisions 87191 via svnmerge from

Merged revisions 87191 via svnmerge from
svn+ssh://pythondev@svn.python.org/python/branches/py3k

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  r87191 | r.david.murray | 2010-12-12 15:06:19 -0500 (Sun, 12 Dec 2010) | 6 lines

  #243654: only create a new MIME boundary if we don't already have one.

  The rearranged code should do exactly what the old code did, but
  the new code avoids a potentially costly re computation in the case
  where a boundary already exists.
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