Fix SF bug #763637, 2.3b2 unpack tuple of wrong size in after_cancel

Tk 8.4 may return different values than 8.3.  This fix should handle
either version.
diff --git a/Misc/NEWS b/Misc/NEWS
index 84da757..479f2e2 100644
--- a/Misc/NEWS
+++ b/Misc/NEWS
@@ -30,6 +30,9 @@
 - SF bug 763023: fix uncaught ZeroDivisionError in difflib ratio methods
   when there are no lines.
 
+- SF bug 763637: fix exception in Tkinter with after_cancel
+  which could occur with Tk 8.4
+
 Tools/Demos
 -----------