When size of terminal window of ssh client is changed, then twisted ssh server throws an exception:

exceptions.AttributeError: TerminalSession instance has no attribute 'windowChanged'

`manhole_ssh.TerminalSession` doesn't implement this method, but according to ISession interface it should.

Is this a bug?

I use insults to create some curses-like ui and I need widgets to be redrawn when the size of window is changed.

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