Updated rubygems to 2.2.1.

=== 2.2.0 / 2013-12-26

Special thanks to Vít Ondruch and Michal Papis for testing and finding bugs in
RubyGems as it was prepared for the 2.2.0 release.

Major enhancements:

* RubyGems can check for gem dependencies files (gem.deps.rb or Gemfile) when
  rubygems executables are started and uses the found dependencies.  This
  means `rake` will work similar to `bundle exec rake`.  To enable this set
  the `RUBYGEMS_GEMDEPS` environment variable to the location of your
  dependencies file.

  See Gem::use_gemdeps for further details.

* A RubyGems directory may now be shared amongst multiple ruby versions.  Upon
  activation RubyGems will automatically compile missing extensions for the
  current platform when the built objects are missing.  Issue #596 by Michal
  Papis

  By default different platforms do not share gem install locations so this
  must be configured by setting GEM_HOME to a common directory.  Some gems use
  fixed paths for requiring extensions and are not compatible with sharing gem
  directories.

  The default sharing location may be configured by RubyGems packagers through
  Gem.default_ext_dir_for.  Pull Request #744 by Vít Ondruch.

Minor enhancements:

* RubyGems checks the 'allowed_push_host' metadata value when pushing a gem to
  prevent an accidental push to a public repository (such as rubygems.org).
  If you have private gems you should set this value in your gem specification
  metadata.  Pull request #603 by Seamus Abshere.
* `gem list` now shows results for multiple arguments.  Pull request #604 by
  Zach Rabinovich.
* `gem pristine --extensions` will restore only gems with extensions.  Issue
  #619 by Postmodern.
* Gem::Specification#files is now sorted.  Pull request #612 by Justin George.
* For `gem list` and friends, "LOCAL" and "REMOTE" headers are omitted if
  only local or remote gem information is requested with --quiet.  Pull
  request #615 by Michal Papis.
* Added Gem::Specification#full_require_paths which is like require_paths, but
  returns a fully-qualified results.  Pull request #632 by Vít Ondruch.
* RubyGems now looks for the https_proxy environment variable for https://
  sources.  RubyGems will fall back to http_proxy if there is no https_proxy.
  Issue #610 by mkristian.
* RubyGems now creates directories in .gem files.  Issue #631 by marksolaris.
* RubyGems raises an exception when a specification includes its gem.  Issue
  #623 by notEthan.
* RubyGems now displays relevant release note information when updating
  RubyGems.  Issue #647 by Trevor Wennblom.
* Deprecated Gem::Installer::ExtensionBuildError in favor of
  Gem::Ext::BuildError.  The old constant is an alias for the new constant.
* When extensions are built the gem_make.out file is always written now, even
  on success.  This will help with debugging bad builds that report success.
* If a specification fails to validate RubyGems shows a link to the
  specification reference guide.  Issue #656 by Markus Heiler.
* When using `gem install -g`, RubyGems now detects the presence of an
  Isolate, Gemfile or gem.deps.rb file.
* Added Gem::StubSpecification#stubbed? to help determine if a user should run
  `gem pristine` to speed up gem loading.  Pull request #694 and #701 by Jon
  Leighton.
* RubyGems now warns when a gem has a pessimistic version dependency that may
  be too strict.
* RubyGems now warns when a gem has an open-ended dependency.
* RubyGems now raises an exception when a dependency for a gem is defined
  twice.
* Marked the license specification attribute as recommended.  Pull request
  #713 by Benjamin Fleischer.
* RubyGems uses io/console instead of `stty` when available.  Pull request
  #740 by Nobuyoshi Nakada
* Relaxed Gem.ruby tests for platforms that override where ruby lives.  Pull
  Request #755 by strzibny.

Bug fixes:

* RubyGems now returns an error status when any file given to `gem which`
  cannot be found.  Ruby bug #9004 by Eugene Vilensky.
* Fixed command escaping when building rake extensions.  Pull request #721 by
  Dmitry Ratnikov.
* Fixed uninstallation of gems when GEM_HOME is a relative directory.  Issue
  #708 by Ryan Davis.
* Default gems are now ignored by Gem::Validator#alien.  Issue #717 by David
  Bahar.
* Fixed typos in RubyGems.  Pull requests #723, #725, #731 by Akira Matsuda,
  pull request #736 by Leo Gallucci, pull request #746 by DV Suresh.
* RubyGems now holds exclusive locks on cached gem files to prevent incorrect
  updates.  Pull Request #737 by Smit Shah
* Improved speed of `gem install --ignore-dependencies`.  Patch by Terence
  Lee.

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