[rubygems/rubygems] Fix `gem pristine etc` resetting gem twice sometimes

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

2 files changed, 12 insertions, 11 deletions

diff --git a/lib/rubygems/basic_specification.rb b/lib/rubygems/basic_specification.rb
index ccd3e49cea..8c75fd41d4 100644
--- a/lib/rubygems/basic_specification.rb
+++ b/lib/rubygems/basic_specification.rb
@@ -100,7 +100,7 @@ class Gem::BasicSpecification
   end
 
   def default_gem?
-    loaded_from &&
+    !loaded_from.nil? &&
       File.dirname(loaded_from) == Gem.default_specifications_dir
   end
 
diff --git a/lib/rubygems/stub_specification.rb b/lib/rubygems/stub_specification.rb
index ea66fbc3f6..4f6a70ba4b 100644
--- a/lib/rubygems/stub_specification.rb
+++ b/lib/rubygems/stub_specification.rb
@@ -83,11 +83,7 @@ class Gem::StubSpecification < Gem::BasicSpecification
   # True when this gem has been activated
 
   def activated?
-    @activated ||=
-      begin
-        loaded = Gem.loaded_specs[name]
-        loaded && loaded.version == version
-      end
+    @activated ||= !loaded_spec.nil?
   end
 
   def default_gem?
@@ -187,11 +183,7 @@ class Gem::StubSpecification < Gem::BasicSpecification
   # The full Gem::Specification for this gem, loaded from evalling its gemspec
 
   def spec
-    @spec ||= if @data
-      loaded = Gem.loaded_specs[name]
-      loaded if loaded && loaded.version == version
-    end
-
+    @spec ||= loaded_spec if @data
     @spec ||= Gem::Specification.load(loaded_from)
   end
   alias_method :to_spec, :spec
@@ -231,4 +223,13 @@ class Gem::StubSpecification < Gem::BasicSpecification
   def sort_obj # :nodoc:
     [name, version, Gem::Platform.sort_priority(platform)]
   end
+
+  private
+
+  def loaded_spec
+    spec = Gem.loaded_specs[name]
+    return unless spec && spec.version == version && spec.default_gem? == default_gem?
+
+    spec
+  end
 end