question: warn about stopped jobs when attempting to exit the shell?

bash:

```
> sleep 5 # type ctrl+z here
[1]+  Stopped                    sleep 5

> exit
exit
There are stopped jobs.
```

schemesh:

```
> sleep 5 # type ctrl+z here
^Z; job  1+ pid  65414 (stopped sigtstp)        {sleep 5}
(stopped sigtstp)

> exit # schemesh exits directly here
```