Merged revisions 77855-77856,77870 via svnmerge from

Merged revisions 77855-77856,77870 via svnmerge from
svn+ssh://pythondev@svn.python.org/sandbox/trunk/2to3/lib2to3

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  r77855 | benjamin.peterson | 2010-01-30 17:32:05 +0100 (Sa, 30 Jan 2010) | 1 line

  don't return node if it is not changed
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  r77856 | benjamin.peterson | 2010-01-30 17:35:29 +0100 (Sa, 30 Jan 2010) | 1 line

  return None to indicate no change
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  r77870 | benjamin.peterson | 2010-01-31 02:21:26 +0100 (So, 31 Jan 2010) | 1 line

  never return the original node given to transform()
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