merge revision(s) r47716: [Backport #10285]

	* ext/stringio/stringio.c (strio_write): ASCII-8BIT StringIO
	  should be writable any encoding strings, without conversion.
	  [ruby-core:65240] [Bug #10285]


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/branches/ruby_2_1@47982 b2dd03c8-39d4-4d8f-98ff-823fe69b080e