Avoid use of File.identical? on files in the source tree

On Windows, this method does not seem to work correctly with files on
network drives (perhaps only WebDAV?).  Presumably, the temporary file
directory is located on the local device.

Author: nobu

test/pathname/test_pathname.rb

@@ -649,14 +649,15 @@ def test_to_s
   end
 
   def test_kernel_open
-    count = 0
-    result = Kernel.open(Pathname.new(__FILE__)) {|f|
-      assert_file.identical?(__FILE__, f)
-      count += 1
-      2
-    }
-    assert_equal(1, count)
-    assert_equal(2, result)
+    token = sprintf("%s\#%s|%d|%.8x", self.class.name, __method__, $$, rand(0x1_0000_0000))
+    Dir.mktmpdir("rubytest-pathname") do |dir|
+      path = Pathname.new(dir) + "file"
+      File.write(path, token)
+      assert_equal(token, File.read(path))
+      assert_equal(token, Kernel.open(path, &:read))
+    ensure
+      File.unlink(path)
+    end
   end
 
   def test_each_filename