prevent more regretful "suspend"

[jidanni]

Regarding
  suspend: suspend [-f]
     Suspend the execution of this shell until it receives a SIGCONT
    signal.  The `-f' if specified says not to complain about this
    being a login shell if it is; just suspend anyway.

My problem is often in an e.g., xterm window I suspend by accident,
forgetting that this is the lowest layer I have made for myself today,
with the only cure being to find the PID number of that shell and send
it a kill -18 from an other window.

Therefore perhaps extend protection to those kind of windows too, not
just login shells.

screen(1) detects this if one trys to do it in a screen window.