Update msgpack to 0.5.9.
2014-07-02 version 0.5.9:
* Support std::tr1 unordered containers by default (#51, #63, #68, #69)
* Remove some warnings (#56)
* Fix segmentation fault after malloc failures (#58, #59)
* Fix alloc/dealloc mismatch (#52, #61)
* Fix sample codes (#60, #64)
* Support implicit conversion from integer to float/double (#54)
* Improve documents (#45, #75, #82, #83)
* Support CMake (#20, #87)
* Remove Ruby dependencies in bootstrap (#86, #87)
* Add FILE* buffer (#40)
* Other bug fixes and refactoring: #39, #73, #77, #79, #80, #81, #84, #90
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