Implement #7566 - os.path.sameopenfile for Windows.

This uses the GetFileInformationByHandle function to return a tuple of values
to identify a file, then ntpath.sameopenfile compares file tuples, which
is exposed as os.path.sameopenfile.
diff --git a/Doc/library/os.path.rst b/Doc/library/os.path.rst
index 317f55a..7aac5c4 100644
--- a/Doc/library/os.path.rst
+++ b/Doc/library/os.path.rst
@@ -251,7 +251,9 @@
 
    Return ``True`` if the file descriptors *fp1* and *fp2* refer to the same file.
 
-   Availability: Unix.
+   Availability: Unix, Windows.
+
+   .. versionchanged:: 3.2 Added Windows support.
 
 
 .. function:: samestat(stat1, stat2)