Log Message:
Update blockdiag to 1.4.7.

1.4.7 (2014-10-21)
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* Fix bugs

  - Fix RuntimeError on unloading plugins

1.4.6 (2014-10-14)
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* Show warnings on loading plugin multiple times
* Unload all plugins on shutdown
* Fix bugs

  - Fix caption is wrapped by paragraph node in reST parser

1.4.5 (2014-10-04)
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* Add node event: build_finished
* Take config object to plugins
* Fix bugs

  - Fix utils.images.get_image_size() does not close an image descriptor

1.4.4 (2014-09-20)
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* :caption: option of blockdiag directive recognizes inline markups
* Fix bugs

  - Fix #58 failed to handle diagram definitions from stdin in py3