* added attr_accessor :http_header_extra that can be used to add extra lines in
  HTTP header.

* added attr_accessor :cookie - shortcut for setting/getting cookies

* added attr_accressor :http_last_response that holds the last HTTP response.
  Usefull when needed to extract information from HTTP header (e.g. cookies,
  keep alive...)


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@4975 b2dd03c8-39d4-4d8f-98ff-823fe69b080e