merge revision(s) 56416: [Backport #12836]
* io.c (copy_stream_body): use IO to write to copy to duplex IO. http://twitter.com/knu/status/786505317974585344
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_3@56569 b2dd03c8-39d4-4d8f-98ff-823fe69b080e
merge revision(s) 56416: [Backport #12836]
git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_3@56569 b2dd03c8-39d4-4d8f-98ff-823fe69b080e