Server now shuts down cleanly on VimClose
Cleaner server shutdown

Listening for VimLeave was sub-optimal. popen.terminate() is much cleaner.
Whitespace fix
Ignoring failed event notifications

These happen rarely and are not a big deal when they do. We still log them to
the Vim message area, but we don't annoy the user with the default, in-your-face
Python traceback.