the tty generated ones (int, quit, tstp), plus term and hup. This makes
command line clients behave on connect(2) where before they would need
to be killed from a different tty. Much easier than making the file
descriptor non-blocking for the duration of connect and then using
pselect/pollts to detect when actual connection or timeout occured using
a different sigmask.
- factor out some of the error paths.