If a default version and a regular version of etc are present at the
same time, RubyGems will end up duplicating work and running pristine
twice.

The `etc` gem is special because it's loaded by RubyGems by default.
When doing this, RubyGems will activate the regularly installed version.
The when `gem pristine` runs, it will find to installed specifications
but materialize both to the already activated specification.

Before:

```
$ gem pristine etc --version 1.4.3
Restoring gems to pristine condition...
Building native extensions. This could take a while...
Restored etc-1.4.3
Building native extensions. This could take a while...
Restored etc-1.4.3
```

After:

```
$ gem pristine etc --version 1.4.3
Restoring gems to pristine condition...
Skipped etc-1.4.3, it is a default gem
Building native extensions. This could take a while...
Restored etc-1.4.3
```

https://github.com/rubygems/rubygems/commit/5c279ac56b

https://github.com/rubygems/rubygems/commit/30f228a97f

https://github.com/rubygems/rubygems/commit/2af077ee38

https://github.com/rubygems/rubygems/commit/67ece7b8b6

Signed-off-by: Takuya Noguchi <takninnovationresearch@gmail.com>

On JRuby, sometimes we get the following error in CI when running a
realworld test that checks that `gem install rails` succeeds:

```
ERROR:  While executing gem ... (NoMethodError)
    undefined method `ignored=' for nil:NilClass
	/home/runner/.rubies/jruby-9.3.2.0/lib/ruby/stdlib/rubygems/stub_specification.rb:193:in `to_spec'
	org/jruby/RubyArray.java:2642:in `map'
	/home/runner/.rubies/jruby-9.3.2.0/lib/ruby/stdlib/rubygems/specification.rb:758:in `_all'
	/home/runner/.rubies/jruby-9.3.2.0/lib/ruby/stdlib/rubygems/specification.rb:956:in `each'
	org/jruby/RubyEnumerable.java:1710:in `any?'
	/home/runner/.rubies/jruby-9.3.2.0/lib/ruby/stdlib/rubygems/resolver/activation_request.rb:111:in `installed?'
	/home/runner/.rubies/jruby-9.3.2.0/lib/ruby/stdlib/rubygems/request_set.rb:173:in `block in install'
```

I'm not sure how this error is happening, but I think there's no need to
copy the `@ignored` instance variable when materializing stub
specifications. This instance variable is used to not print a warning
about missing extensions more than once for each gem upon gem
activation, but as far as I can see, it's only used by methods that work
on specification stubs. Once specifications are materialized, I think
it can be safely ignored.

https://github.com/rubygems/rubygems/commit/301cecd5a7

This changes "test/rubygems/test_case.rb" to "test/rubygems/helper.rb",
and "test/rubygems/test_utilities.rb" to "test/rubygems/utilities.rb".

The two files are a helper for tests, not test files. However, a file
starting with "test_" prefix is handled as a test file directly loaded
by test-unit because Rakefile specifies:

```
t.test_files = FileList['test/**/test_*.rb']
```

Directly loading test/rubygems/test_utilities.rb caused "uninitialized
constant Gem::TestCase". This issue was fixed by
59c682097197fee4052b47e4b4ab86562f3eaa9b, but the fix caused a
"circular require" warning because test_utilities.rb and test_case.rb
are now requiring each other.

Anyway, adding "test_" prefix to a test helper file is confusing, so
this changeset reverts the fix and solve the issue by renaming them.

https://github.com/rubygems/rubygems/commit/6460e018df

https://github.com/rubygems/rubygems/commit/c77868a555