Do not call event_del() for signals after fork(), just use sigaction()
directly instead - calling libevent functions after fork() w/o
event_reinit() is a bad idea, even if in this case it was harmless.
Catch SIGHUP and terminate if running as a client. This prevents clients
from being left hanging around when, for example, a SSH session is
disconnected.
ok nicm@
Make signal handler setup/teardown two common functions instead of six,
and reset SIGCHLD after fork to fix problems with some shells. From
Romain Francoise.
