Update Encode to CPAN version 2.51

Update Encode to CPAN version 2.51

  [DELTA]

$Revision: 2.51 $ $Date: 2013/04/29 22:19:11 $
! Encode.xs
  Addressed: Encode.xs doesn't compile with Microsoft C compiler
  https://rt.cpan.org/Public/Bug/Display.html?id=84920
! MANIFEST
  Addressed: t/taint.t missing
  https://rt.cpan.org/Public/Bug/Display.html?id=84919

2.50 2013/04/26 18:30:46
! Encode.xs Unicode/Unicode.xs
  lib/Encode/Unicode/UTF7.pm lib/CN/HZ.pm lib/Encode/GSM0338.pm
  t/taint.t
  Addressed: Encode::encode and Encode::decode
             gratuitously launders tainted data
  Taintedness now propagates as it should.
  https://rt.cpan.org/Ticket/Display.html?id=84879
! encoding.pm
  Addressed: 5.18 deprecation
  https://rt.cpan.org/Ticket/Display.html?id=84709
! bin/piconv
  Applied: Update piconv documentation
  https://rt.cpan.org/Ticket/Display.html?id=84695