[2.7] bpo-34162: Update 2.7 idlelib/NEWS.txt to 2018-9-24 (GH-9550)

Lib/idlelib/NEWS.txt

+Since 2.7.13, only severe bugs are fixed on the 2.7 branch.
+
+What's New in IDLE 2.7.16?
+==========================
+*Release date: 2019-01-01?*
+
+bpo-34275: Make calltips always visible on Mac.
+Patch by Kevin Walzer.
+
+bpo-34120: Fix freezing after closing some dialogs on Mac.
+This is one of multiple regressions from using newer tcl/tk.
+
+
 What's New in IDLE 2.7.13?
 ==========================
-*Release date: 2017-01-01?*
+*Release date: 2016-12-17*
 
 - Issue #27854: Make Help => IDLE Help work again on Windows.
   Include idlelib/help.html in 2.7 Windows installer.
@@ -35,7 +48,7 @@ What's New in IDLE 2.7.13?
 
 What's New in IDLE 2.7.12?
 ==========================
-*Release date: 2015-06-25*
+*Release date: 2016-06-25*
 
 - Issue #5124: Paste with text selected now replaces the selection on X11.
   This matches how paste works on Windows, Mac, most modern Linux apps,