bpo-29910: IDLE no longer deletes a character after commenting out a region (#825)

This happened because shortcut has a class binding and 'break' was not returned.
Fix other potential conflicts between IDLE and default key bindings.

* Add news item

* Update NEWS
diff --git a/Lib/idlelib/runscript.py b/Lib/idlelib/runscript.py
index 79d86ad..3355f17 100644
--- a/Lib/idlelib/runscript.py
+++ b/Lib/idlelib/runscript.py
@@ -63,6 +63,7 @@
             return 'break'
         if not self.tabnanny(filename):
             return 'break'
+        return "break"
 
     def tabnanny(self, filename):
         # XXX: tabnanny should work on binary files as well