Remove unused main_thread parameter from Thread::create
Remove unused -Xthread.debug option

Debugging information for threads is set at compile time
not runtime. This patch removes the unused -Xthread.debug option
along with two redundant messages that were already controlled
by the cDebugThreading variable set at compile time.
Added other standard lib gems.
Added spec for #require of .rb vs .<dlext>.
Removed config_version hackery.
Fixed #require to load .rb before c-ext.
Reworked requiring pre-installed gems.
Ignore rake clean if not configured.
Add dates to changelog
Added failing spec for BasicObject::BasicObject.

This was added as a starting point for #2828.
Changed description of failing BasicObject spec.
BasicObject can refer to BasicObject from within itself.
Untagged passing spec.
Removed special case obsoleted by 0bdf028.
Remove no longer needed convert_to_name(s) methods
Removed psych from pre-installed gems.

On Heroku, when pushing a Ruby app, libyaml is installed if psych is detected
in the Gemfile or bundling process (I'm not sure which). This means that if
psych is pre-installed, rubygems will cause it to be loaded vi YAML and libyaml
won't be available, which means we can't run to install psych and Heroku can't
see that psych is being used...

Heroku could just install libyaml always and this wouldn't be an issue.
Updated RubyGems to 2.2.2.

RubyGems 2.2.2 installed

=== 2.2.1 / 2014-01-06

Bug fixes:

* Platforms in the Gemfile.lock GEM section are now handled correctly.  Bug
  #767 by Diego Viola.
* RubyGems now displays which gem couldn't be uninstalled from the home
  directory.  Pull request #757 by Michal Papis.
* Removed unused method Gem::Resolver#find_conflict_state.  Pull request #759
  by Smit Shah.
* Fixed installing gems from local files without dependencies.  Issue #760 by
  Arash Mousavi, pull request #764 by Tim Moore.
* Removed TODO about syntax that works in Ruby 1.8.7.  Pull request #765 by
  Benjamin Fleischer.
* Switched Gem.ruby_api_version to use RbConfig::CONFIG['ruby_version'] which
  has the same value but is overridable by packagers through
  --with-ruby-version= when configuring ruby.  Bug #770 by Jeremy Evans.
* RubyGems now prefers the bundler API for `gem install` to reduce HTTP
  requests.  (This change was intended for RubyGems 2.2.0 but was missed.)
  This should address bug #762 by Dan Peterson and bug #766 by mipearson.
* Added Gem::BasicSpecification#source_paths so documentation or analysis
  tools can work properly as require_paths no longer returns extension source
  directories.  Bug #758 Vít Ondruch.
* Gem.read_binary can read read-only files again.  This caused file://
  repositories to stop working.  Bug #761 by John Anderson.
* Fixed specification file sorting for Ruby 1.8.7 compatibility.  Pull
  request #763 by James Mead
Updated Changelog.
Bumped version to 2.2.5.
Reset release date.