bug#69819: 30.0.50; comint-mode does not always respect the read-only flag

[Dima Kogan]

> What expectation, exactly? The buffer is not changed; the process is
> terminated, but that's not the same as changing the process's buffer!

The buffer IS changed, actually: when the inferior process dies, it
prints a message into the buffer:

  Process shell<1> finished

But that's a red herring I think: if the inferior process died, but the
printing was blocked by the read-only mode, I would still consider that
to be a bug.

My use case is this. I use shell-mode buffers extensively. Periodically
I want to examine the output of some command in a *shell* buffer:
compare it against other data, look at it, cut/paste it, whatever. While
I'm doing that I don't want to accidentally change anything, so I C-x
C-q. Then accidental keystrokes don't end up changing anything. UNLESS
that accidental keystroke is C-d (and probably a few others I haven't
hit by mistake yet). This use case and expectation seems reasonable to
me.

Thanks.