Make it possible to know whether termdown was closed manually.

[crocket]

I chain termdown with an alarm command.
When termdown is closed manually or crashed, I don't want the alarm command to be executed.

When termdown is crashed, exit status is not 0.
Thus, if termdown exits with non-zero exit status when I close it manually, I'd be able to detect whether termdown was closed manually or crashed.

There could be other ways to detect whether termdown was closed manually.

[crocket]

It seems I can just press Ctrl+C to close the chain.