Ruby

• ext/json/json.gemspec, lib/rdoc/rdoc.gemspec: added gemspec directly.
• defs/default_gems, tool/rbinstall.rb: removed default_gems definition.
  it make simple installation for default gems.

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@50269 b2dd03c8-39d4-4d8f-98ff-823fe69b080e