Simplify and make more clear comment on os.open.

certbot/compat/os.py

@@ -31,13 +31,11 @@ std_sys.modules[__name__ + '.path'] = path
 del ourselves, std_os, std_sys
 
 
-# The os.open function on Windows will have the same effect than a bare os.chown towards the given
-# mode, and will create a file with the same flaws that what have been described for os.chown.
-# So upon file creation, security.take_ownership will be called to ensure current user is the owner
-# of the file, and security.chmod will do the same thing than for the modified os.chown.
-# Internally, take_ownership will update the existing metadata of the file, to set the current
-# username (determined by the win32api module) as the owner of the file.
+# The os.open function on Windows has the same effect than a call to os.chown concerning the file
+# modes: these modes lack of a correct control over the permissions given to the file. Instead,
+# filesystem.open invokes filesystem.take_ownership and filesystem.chown to ensure that both owner
+# and permissions are correctly set.
 def open(*unused_args, **unused_kwargs):  # pylint: disable=function-redefined
     """Method os.open() is forbidden"""
-    raise RuntimeError('Usage of os.open() is forbidden. '  # pragma: no cover
+    raise RuntimeError('Usage of os.open() is forbidden. '
                        'Use certbot.compat.filesystem.open() instead.')