Return correct exit code upon signal + SIGQUIT now quits without cleanup

See http://www.tldp.org/LDP/abs/html/exitcodes.html, http://www.gnu.org/software/libc/manual/html_node/Termination-Signals.html

Now SIGQUIT actually quits without cleaning up. Which is very useful for debug and do not impact people using process managers (upstart, systemd, etc)