Passing `binmode: true` to `IO.pipe` should behave like `binmode`

When passing `binmode: true` to `IO.pipe`, it should behave the same way
as calling `binmode` on each of the file handles.  It should set the
file to binmode *and* set the encoding to binary on the file.

Before this commit, passing `binmode: true` to `IO.pipe` would make
`binmode?` return `true`, but the file's encoding would remain the same
as the default encoding.  Passing `binmode: true` should make `binmode?`
return `true` *and* set the encoding to binary.

io.c

@@ -10312,6 +10312,12 @@ rb_io_s_pipe(int argc, VALUE *argv, VALUE klass)
     rb_io_synchronized(fptr2);
 
     extract_binmode(opt, &fmode);
+
+    if (fmode & FMODE_BINMODE) {
+	rb_io_ascii8bit_binmode(r);
+	rb_io_ascii8bit_binmode(w);
+    }
+
 #if DEFAULT_TEXTMODE
     if ((fptr->mode & FMODE_TEXTMODE) && (fmode & FMODE_BINMODE)) {
 	fptr->mode &= ~FMODE_TEXTMODE;

test/ruby/test_io.rb

@@ -113,6 +113,38 @@ class TestIO < Test::Unit::TestCase
     ].each{|thr| thr.join}
   end
 
+  def test_binmode_writer
+    EnvUtil.with_default_internal(Encoding::UTF_8) do
+      reader, writer = IO.pipe
+      reader.binmode
+      writer.binmode
+
+      reader2, writer2 = IO.pipe(binmode: true)
+
+      assert writer.binmode?
+      assert writer2.binmode?
+      assert_equal writer.binmode?, writer2.binmode?
+      assert_equal writer.external_encoding, writer2.external_encoding
+      assert_equal writer.internal_encoding, writer2.internal_encoding
+    end
+  end
+
+  def test_binmode_reader
+    EnvUtil.with_default_internal(Encoding::UTF_8) do
+      reader, writer = IO.pipe
+      reader.binmode
+      writer.binmode
+
+      reader2, writer2 = IO.pipe(binmode: true)
+
+      assert reader.binmode?
+      assert reader2.binmode?
+      assert_equal reader.binmode?, reader2.binmode?
+      assert_equal reader.external_encoding, reader2.external_encoding
+      assert_equal reader.internal_encoding, reader2.internal_encoding
+    end
+  end
+
   def test_pipe_block
     x = nil
     ret = IO.pipe {|r, w|