2015-06-23 io.js v2.3.1 Release

PR-URL: https://github.com/nodejs/io.js/pull/1996

Notable changes

* module: The number of syscalls made during a require() have been
  significantly reduced again (see #1801 from v2.2.0 for previous
  work), which should lead to a performance improvement
  (Pierre Inglebert) #1920.
* npm:
  - Upgrade to v2.11.2 (Rebecca Turner) #1956.
  - Upgrade to v2.11.3 (Forrest L Norvell) #2018.
* zlib: A bug was discovered where the process would abort if the
  final part of a zlib decompression results in a buffer that would
  exceed the maximum length of 0x3fffffff bytes (~1GiB). This was
  likely to only occur during buffered decompression (rather than
  streaming). This is now fixed and will instead result in a thrown
  RangeError (Michaël Zasso) #1811.