Issue #5117: Case normalization was needed on ntpath.relpath(). And
fixed root directory issue on posixpath.relpath(). (Ported working fixes
from ntpath)
diff --git a/Lib/test/test_ntpath.py b/Lib/test/test_ntpath.py
index 5609aee..237aec0 100644
--- a/Lib/test/test_ntpath.py
+++ b/Lib/test/test_ntpath.py
@@ -238,6 +238,7 @@
         tester('ntpath.relpath("/", "/")', '.')
         tester('ntpath.relpath("/a", "/a")', '.')
         tester('ntpath.relpath("/a/b", "/a/b")', '.')
+        tester('ntpath.relpath("c:/foo", "C:/FOO")', '.')
 
     def test_sameopenfile(self):
         with TemporaryFile() as tf1, TemporaryFile() as tf2: