Blocked revisions 64016,64018-64019 via svnmerge

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  r64016 | georg.brandl | 2008-06-07 16:16:12 +0000 (Sat, 07 Jun 2008) | 2 lines

  Register IterableUserDict as a MutableMapping.
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  r64018 | georg.brandl | 2008-06-07 17:03:28 +0000 (Sat, 07 Jun 2008) | 2 lines

  #3057: Fix the MutableMapping ABC to use the 2.6 dict interface.
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  r64019 | georg.brandl | 2008-06-07 17:11:00 +0000 (Sat, 07 Jun 2008) | 2 lines

  Backport docs for abc module to 2.6.
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