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/library/socket/unixserver/accept_nonblock_spec.rb

@@ -0,0 +1,40 @@
+require File.expand_path('../../../../spec_helper', __FILE__)
+require File.expand_path('../../fixtures/classes', __FILE__)
+
+describe "UNIXServer#accept_nonblock" do
+
+  platform_is_not :windows do
+    before :each do
+      @path = SocketSpecs.socket_path
+      rm_r @path
+
+      @server = UNIXServer.open(@path)
+      @client = UNIXSocket.open(@path)
+
+      @socket = @server.accept_nonblock
+      @client.send("foobar", 0)
+    end
+
+    after :each do
+      @socket.close
+      @client.close
+      @server.close
+      rm_r @path
+    end
+
+    it "accepts a connection in a non-blocking way" do
+      data = @socket.recvfrom(6).first
+      data.should == "foobar"
+    end
+
+    it "returns a UNIXSocket" do
+      @socket.should be_kind_of(UNIXSocket)
+    end
+
+    ruby_version_is '2.3' do
+      it 'returns :wait_readable in exceptionless mode' do
+        @server.accept_nonblock(exception: false).should == :wait_readable
+      end
+    end
+  end
+end