* string.c: [DOC] Description of rb_str_equal [Fixes GH-375]
  Based on a patch by @markijbema
  https://github.com/ruby/ruby/pull/375


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@42417 b2dd03c8-39d4-4d8f-98ff-823fe69b080e