core: rework when we kill with which signal

core: rework when we kill with which signal

When the user wants to explicitly send our own PID a signal, then do so.

Don't follow up SIGABRT with a SIGHUP if send_sighup is enabled. At that
point the process should have segfaulted, hence there's no point in
following up with a SIGHUP.

Send only termination signals to ourselves, never KILL or ABRT signals.