[Twisted-Python] Screen clearing in the Manhole

[Peter Westlake]

I found it!

Manhole.terminalSize, inherited from RecvLine, does
self.terminal.eraseDisplay(). 
t.c.manhole_ssh.TerminalSessionTransport.__init__ calls terminalSize
*after* makeConnection.

Since setting the terminal size is a sensible thing to do, and it can't
be done before the connection is made, I'm not sure that much can be
done about this. I was able to make my message stay visible by
overriding terminalSize with a version that didn't erase, but that isn't
very clean or general.

Peter.