* lib/open-uri.rb: Support multiple fields with same field
  name (like Set-Cookie).
  (OpenURI::Meta#metas): New accessor to obtain fields as a Hash from
  field name (string) to field values (array of strings).
  [ruby-core:37734] [Bug #4964] reported by ren li.



git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@40207 b2dd03c8-39d4-4d8f-98ff-823fe69b080e