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). It is also the way the signal should be handled according to GNU.