Add a vi mode line to common.py.
Add a vi mode line to common.py.

git-svn-id: a751b5b3dcfba0ee4592a85c40d2fdd063ca0d53@480 4ff78f4a-9131-11de-b045-6380ec9940d4

XiaonuoGantan/pywebsocket,XiaonuoGantan/pywebsocket