block signals, if available. If HAVE_VFORK, save and restore
signal handlers that the child might change, since in many
systems (e.g. Solaris 2.4) if the child changes the signal
block signals, if available. If HAVE_VFORK, save and restore
signal handlers that the child might change, since in many
systems (e.g. Solaris 2.4) if the child changes the signal