2015-05-31 io.js v2.2.0 Release

PR-URL: https://github.com/nodejs/io.js/pull/1808

Notable Changes:

* node: Speed-up require() by replacing usage of fs.statSync() and
  fs.readFileSync() with internal variants that are faster for this use-case
  and do not create as many objects for the garbage collector to clean up.
  The primary two benefits are: significant increase in application start-up
  time on typical applications and better start-up time for the debugger by
  eliminating almost all of the thousands of exception events.
  (Ben Noordhuis) #1801.
* node: Resolution of pre-load modules (-r or --require) now follows the
  standard require() rules rather than just resolving paths, so you can now
  pre-load modules in node_modules. (Ali Ijaz Sheikh) #1812.
* npm: Upgraded npm to v2.11.0. New hooks for preversion, version, and
  postversion lifecycle events, some SPDX-related license changes and license
  file inclusions. See the release notes for full details.