2015-06-01 io.js v2.2.1 Release

PR-URL: https://github.com/nodejs/io.js/pull/1856

Notable Changes:

* http: reverts the removal of an undocumented `client` property on client
  connections, this property is being used in the wild, most notably by
  https://github.com/request/request which is used by npm.
  (Michaël Zasso) [#1852](nodejs#1852).