Fix for issue #10406: enable Rstrip extension on OSX

Without this patch the Rstrip extension for IDLE is not enabled on OSX,
while it is enabled on other platforms.

Patch by Ned Deily.
diff --git a/Misc/NEWS b/Misc/NEWS
index 8058a2f..0481ddc 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -18,6 +18,9 @@
 
 - Issue #10107: Warn about unsaved files in IDLE on OSX.
 
+- Issue #10406: Enable Rstrip IDLE extension on OSX (just like on other
+  platforms).
+
 - Issue #10478: Reentrant calls inside buffered IO objects (for example by
   way of a signal handler) now raise a RuntimeError instead of freezing the
   current process.