Add in-tree mspec and ruby/spec

* For easier modifications of ruby/spec by MRI developers.
* .gitignore: track changes under spec.
* spec/mspec, spec/rubyspec: add in-tree mspec and ruby/spec.
  These files can therefore be updated like any other file in MRI.
  Instructions are provided in spec/README.
  [Feature #13156] [ruby-core:79246]

git-svn-id: svn+ssh://ci.ruby-lang.org/ruby/trunk@58595 b2dd03c8-39d4-4d8f-98ff-823fe69b080e

spec/rubyspec/core/file/setgid_spec.rb

@@ -0,0 +1,36 @@
+require File.expand_path('../../../spec_helper', __FILE__)
+require File.expand_path('../../../shared/file/setgid', __FILE__)
+
+describe "File.setgid?" do
+  it_behaves_like :file_setgid, :setgid?, File
+end
+
+describe "File.setgid?" do
+  before :each do
+    @name = tmp('test.txt')
+    touch @name
+  end
+
+  after :each do
+    rm_r @name
+  end
+
+  it "returns false if the file was just made" do
+    File.setgid?(@name).should == false
+  end
+
+  it "returns false if the file does not exist" do
+    rm_r @name # delete it prematurely, just for this part
+    File.setgid?(@name).should == false
+  end
+
+  as_superuser do
+    platform_is_not :windows do
+      it "returns true when the gid bit is set" do
+        system "chmod g+s #{@name}"
+
+        File.setgid?(@name).should == true
+      end
+    end
+  end
+end