Revert r42938 "* lib/rubygems: Update to RubyGems 2.1.3"

It breaks build.
20130913T200302Z.diff.html.gz

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@42941 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

lib/rubygems/commands/unpack_command.rb

@@ -34,6 +34,24 @@ class Gem::Commands::UnpackCommand < Gem::Command
     "--version '#{Gem::Requirement.default}'"
   end
 
+  def description
+    <<-EOF
+The unpack command allows you to examine the contents of a gem or modify
+them to help diagnose a bug.
+
+You can add the contents of the unpacked gem to the load path using the
+RUBYLIB environment variable or -I:
+
+  $ gem unpack my_gem
+  Unpacked gem: '.../my_gem-1.0'
+  [edit my_gem-1.0/lib/my_gem.rb]
+  $ ruby -Imy_gem-1.0/lib -S other_program
+
+You can repackage an unpacked gem using the build command.  See the build
+command help for an example.
+    EOF
+  end
+
   def usage # :nodoc:
     "#{program_name} GEMNAME"
   end