Keep IDLE from displaying spurious SystemExit tracebacks

when running scripts that terminated by raising SystemExit
(i.e. unittest and turtledemo).

Lib/idlelib/run.py

@@ -301,11 +301,14 @@ class Executive(object):
                 exec code in self.locals
             finally:
                 interruptable = False
+        except SystemExit:
+            # Scripts that raise SystemExit should just
+            # return to the interactive prompt
+            pass
         except:
             self.usr_exc_info = sys.exc_info()
             if quitting:
                 exit()
-            # even print a user code SystemExit exception, continue
             print_exception()
             jit = self.rpchandler.console.getvar("<<toggle-jit-stack-viewer>>")
             if jit: