Ensure we never call anything after "Close".

Ensure we never call anything after "Close".

The only valid commands on a close pane are "Close", "Close:mark", and
"Notify:Close" and these are always pane_call.  So blocks all other
calls on DAMAGED_CLOSED panes, and block even these on DAMAGED_DEAD.

Note that "Free" is also allowed, but will soon be gone.

This requires that home_comm_call() must be supported so that a comm can
be called with a recently-closed pane as the focus (assuming it won't be
dereferenced).

Signed-off-by: NeilBrown <neil@brown.name>