Treat input of Marshal.load as binary

spec/core/marshal/shared/load.rb

@@ -798,11 +798,9 @@ def io.binmode; raise "binmode"; end
     it "loads a String as BINARY if no encoding is specified at the end" do
       str = "\xC3\xB8".dup.force_encoding("BINARY")
       data = "\x04\b\"\a\xC3\xB8".dup.force_encoding("UTF-8")
-      NATFIXME 'loads a String as BINARY if no encoding is specified at the end', exception: ArgumentError, message: 'marshal data too short' do
-        result = Marshal.send(@method, data)
-        result.encoding.should == Encoding::BINARY
-        result.should == str
-      end
+      result = Marshal.send(@method, data)
+      result.encoding.should == Encoding::BINARY
+      result.should == str
     end
 
     it "raises ArgumentError when end of byte sequence reached before string characters end" do

src/marshal.rb

@@ -564,10 +564,10 @@ def read_byte
     end
 
     def read_bytes(integer)
-      if @source.length - @offset >= integer
-        string = @source.slice(@offset, integer)
+      if @source.bytesize - @offset >= integer
+        string = @source.byteslice(@offset, integer)
         @offset += integer
-        string
+        string.b
       else
         raise ArgumentError, 'marshal data too short'
       end