SSH connection hanging on logout

[John Bowman]

> > > i think that shutdown should only be allowed if c->istate ==
> > > CHAN_INPUT_CLOSED;
> > 
> > No, this will cause openssh to hang under interactive use.
> 
> but the transition from CHAN_INPUT_CLOSED to state!=CHAN_INPUT_CLOSED
> should be caused by shutdown.  see nchan2.ms
> 
If c->istate is CHAN_INPUT_CLOSED, then shutdown won't be called in any case.