merge r47598 partially. extracted commits are as follows. [Bug #9728]
https://github.com/k-takata/Onigmo/commit/15ddec6d18e27fdc1988236764e766fd5892ecf5


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_1@47954 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
* 2014-10-16

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_1@47955 b2dd03c8-39d4-4d8f-98ff-823fe69b080e