maintainability.
* test/rubygems/test_gem_commands_query_command.rb:  Note default gems
  in gem list details.

* lib/rubygems/uninstaller.rb:  Detect all gems for uninstallation.
  This allows duplicate installs of default gems to be removed.
* lib/rubygems/specification.rb:  Allow use of ::each_spec.
* lib/rubygems/test_case.rb:  Added install_default_gems.
* test/rubygems/test_gem_commands_uninstall_command.rb:  Moved test
  down to the uninstaller tests.
* test/rubygems/test_gem_uninstaller.rb:  Test for uninstallation of
  default gems and duplicate default gems.


git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@38461 b2dd03c8-39d4-4d8f-98ff-823fe69b080e