Log Message:
Update msgpack-python to 0.4.6.

0.4.6
=====
:release date: 2015-03-13

Bugs fixed
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* fallback.Unpacker: Fix Data corruption when OutOfData.
  This bug only affects "Streaming unpacking."

0.4.5
=====
:release date: 2015-01-25

Bugs fixed
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* Fix test failure on pytest 2.3.  (by @ktdreyer)
* Fix typos in ChangeLog.  (Thanks to @dmick)
* Improve README.rst  (by @msabramo)